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November 5

Lethal overdose of Caffeine - biological process involved?

Recently a young man in the UK accidentally killed himself by ingesting two spoonfuls of caffeine powder. I was wondering about the mechanism by which a caffeine overdose actually kills you, as the news report didn't mention really how he died. The caffeine article mentions extreme amounts of caffeine can cause ventricular fibrillation. Does this mean your heart just kinda starts beating all out of rhythm, screwing up your blood flow, and thereby leading to death via asphyxiation? The Masked Booby (talk) 00:37, 5 November 2010 (UTC)

As the article you linked to states, v-fib results in "cessation of effective blood circulation". Asphyxiation means the air supply is cut off. In this case, that is not true...the oxygenated blood is just mostly sitting there rather than flowing to cells. The cells are starved for oxygen and soon start dying (or at least some of the most important ones do), so it's a similar effect to having no air supply, but a different chain of events. DMacks (talk) 01:16, 5 November 2010 (UTC)

Here's the article about the death. When are the ACMD going to issue a report on caffeine then? "This should serve as a warning that caffeine is so freely available on the internet but so lethal if the wrong dosage is taken” reminds me of other things. SmartSE (talk) 01:28, 5 November 2010 (UTC)

Other caffeine overdoses can cause "rhabdomyolysis and acute renal failure" [1] but reading the abstracts on google scholar it has caused deaths in a wide variety of ways. SmartSE (talk) 01:35, 5 November 2010 (UTC)

Thanks everyone! The Masked Booby (talk) 04:53, 5 November 2010 (UTC)

mosquito

Hello,

pls i would like to cofirm if it is true that an average mosquito has 47 teeth?

Thanks —Preceding unsigned comment added by 62.173.41.242 (talk) 00:53, 5 November 2010 (UTC)

Mosquitos have mouthparts designed to pierce into skin, so they wouldn't have teeth in the normal sense. --Chemicalinterest (talk) 00:57, 5 November 2010 (UTC)

Mosquitoes are actually nectar feeders - see Mosquito#Feeding habits of adults. In female mosquitoes (only) they can also pierce the skin and suck blood - see Insect mouthparts#Piercing and Sucking Insects. They don't have teeth as such. This site gives some pretty nice 'close-ups' of their mouthparts. --jjron (talk) 07:14, 5 November 2010 (UTC)

There are 47 SPECIES of mosquitoes. I know because where I live there are all 47 of them! —Preceding unsigned comment added by 165.212.189.187 (talk) 17:58, 5 November 2010 (UTC)

In case anyone is wondering, the OP has probably stumbled across one of those trivia list that infest webpages and inboxes with information of dubious quality. I've seen the 47 teeth thing a number of times, and virtually uniquely among these sorts of list the quantity is actually attributed (to Isaac Asimov of all people). Here is an example. 64.235.97.146 (talk) 19:19, 5 November 2010 (UTC)

Which of Isaac Asimov's two jobs (that of a research biochemist and that of a science fiction writer) makes him trustworthy regarding the mouthparts of insects? --Jayron32 20:36, 5 November 2010 (UTC)

Asimov was a wide ranging and prolific science populariser (as well as dipping into several Humanities topics) by virtue of being a good textual researcher - much like we here on the RefDesks! Just because the claim is attributed to him doesn't mean he actually said it - I've read a good deal (though by no means all) of his non-fiction and would have noticed such a ridiculous mis-statement, but never have. Until someone comes up with a citation I'll assume the attribution is as erroneous as the "fact." 87.81.230.195 (talk) 22:09, 5 November 2010 (UTC)

Mosquitoes may not have the same kind of teeth that vertebrates have, with enamel and dentin, but the mouthparts of female mosquitoes do indeed have structures on their maxillae which are called teeth, which look like little saw teeth.

The question is complicated by there being 3,500 species of mosquitoes, whose maxillae vary considerably. Indeed, it has been suggested([2], page 508) that the number of teeth a mosquito has could be used as an aid in taxonomy. Mosquitoes with 14 or fewer teeth per maxilla can be expected to feed primarily on man, whereas those with more teeth could be able to feed on domestic animals.(ibid) Also, the number of teeth in individuals within a species can vary a bit, for example, the W. smithii mosquitoes examined in the given reference had between 8-10 teeth per maxilla. Since those mosquitoes that have maxillae have two of them, 14 teeth per maxilla amounts to a mosquito having a total of 28 teeth. However, due to the huge number of mosquito species, and due to a bit of variability of number of teeth per individual within a species, there almost certainly do exist at least some individual mosquitoes which have 47 teeth, as that’s easily within the typical ballpark. Red Act (talk) 08:39, 6 November 2010 (UTC)

Oops, I missed the word "average" in the OP. From what I've read, 47 sounds a bit high for the number of teeth an average mosquito that bites humans has, but not by a huge amount. And it's a bit vague as to what "average" means here; are you counting by number of species, or number of individuals, or number of bites of humans? Red Act (talk) 08:58, 6 November 2010 (UTC)

Yes, as was displayed in the external link I gave in my original answer. These are not teeth in any sense of common usage of the term though, that is in the sense of their biological function, they are just given that name. But I spose you could ask "how many teeth does the average comb have" and get an answer as well. However, even if we took that as reasonable, the 47 still adds further silliness, as since mosquitoes are bilaterally symmetrical we would expect them to have an even number of teeth. So then we would have to expect that this is some overall average (of what?), with as much meaning as saying the average mammal has 19.574* teeth (* invented figure). --jjron (talk) 16:55, 6 November 2010 (UTC)

I disagree that mosquito teeth have no similarity in biological function to vertebrate teeth. Consider the description "a series of features on an animal's maxilla which are used to cut the flesh of another animal during the process of feeding". That description could be referring to the incisors on a human maxilla (our upper jaw) during the process of biting off a piece of fried chicken. That same description could also be used to describe the teeth on a mosquito's maxillae and their function during the piercing process. That wouldn't be obvious from the picture in the link you gave in which the maxillary teeth are identified, because in that picture the proboscis is still covered with the labium. But the labium does not enter the skin during the piercing process. During the piercing process, the maxillae are on the outside of the fascicle, with the teeth facing the flesh, slicing it. The article you linked to says that "the teeth cause more damage once inside the delicate tissues below the skin and thus cause a greater haemorrhage than would a straight, smooth, needle-like appendage". And the page I linked to says "Gordon and Lumsden (1939) and Waldbauer (1962) considered that the maxillary teeth may assist the entry of the fascicle by cutting through the tissue during protraction". The functioning of incisors and a mosquito's maxillary teeth is a bit different in that incisors cut flesh kind of like a pair of scissors, whereas a mosquito's maxillary teeth cut flesh more like a saw or a serrated knife, but they still are both used to cut the flesh of another animal while feeding. And if a difference in the details like that of exactly how two things perform a particular biological function is enough for you to say that it's a completely different biological function, then you'd also have to say that "mosquitoes don't have eyes as such", because the details of how mosquito eyes perform their function differs considerably from the way human eyes perform their function.

I'm using the phrase "maxillary teeth" above because I found out that some mosquito larvae also have mandibular teeth, which "serve as masticating agents by grinding food"[3]. That description would also work as a description of molars in vertebrates, so that's another example of there existing mosquito teeth which perform a similar biological function to a vertebrate's teeth.

Saying that the average of 47 adds further silliness because mosquitoes have an even number of teeth is very much like saying that the statistic that the average family has 2 1/2 children is silly, because no family has a half a kid. Unless otherwise specified, "average" generally means the mean (as opposed to the median or the mode), and there is no presumption that the mean of a set will coincidentally happen to be an element of that set. Red Act (talk) 04:37, 7 November 2010 (UTC)

Whatever became of the "super focused sound" guy and his invention?

I recall reading several years ago about an inventor, perhaps in California?, who invented a way to focus sound such that if two people were standing shoulder to shoulder only one would hear the music projected from a device in front of them. The effect was so profound as to be at first unbelievable. (You guys really didn't hear that too?!?) I also recall advertising companies being very interested it, as it was purported to allow them to play targeted audio ads without filling the ambient environment with background noise. One of the articles mentioned walking past posters in a subway with each poster talking "to you" as you passed, but people outside the "beam" hearing nothing. Does this jog anyone's memory? I'd love to know what the current status of that invention is... The Masked Booby (talk) 04:50, 5 November 2010 (UTC)

The guy you're talking about is Woody Norris; see Sound from ultrasound. Red Act (talk) 05:40, 5 November 2010 (UTC)

The guy you're thinking of perhaps also might be F. Joseph Pompei of Holosonics, who is the one who actually solved the distortion problems of earlier systems, and beat Woody Norris to the market by a couple of years. But Woody Norris appears to have gotten the most famous for it, so you're probably thinking of him.

This is consistent with my impression of inventions in general. Contrary to popular perception, if you look at any major invention, the invention process is typically a complicated mess in which there really isn't one person who is really the inventor of the thing, and the person who becomes famous for being "the" inventor of the thing is not at all necessarily the first person to have created that type of thing. See, e.g., Invention of the telephone, Invention of radio, Electrical telegraph or Incandescent light bulb#History of the light bulb. Red Act (talk) 06:41, 5 November 2010 (UTC)

I don't know about that specifically, but some museums have systems where a parabolic dish in the ceiling projects sound down so that only the person standing directly in front of a particular exhibit can hear it. The effect is a bit startling. APL (talk) 13:38, 5 November 2010 (UTC)

Sound Refreshment Station, of which six are located in the departure areas at Oslo Airport, Gardermoen, are sound "showers" that make refreshing sounds audible only to a person immediately under them. Cuddlyable3 (talk) 14:33, 5 November 2010 (UTC)

"The decision to axe the Ark will leave the Navy without the capability of launching fixed wing aircraft."

What about its sister ship, the HMS Illustrious? Did the BBC become so unreliable, or is there something I missed? By the way, why would the British Navy decommission all their fixed wing aircrafts? If Argentina invades the Falklands again, the plan is to use only helicopters against their air force? --131.188.3.20 (talk) 11:21, 5 November 2010 (UTC)

According to HMS Illustrious, "As part of Strategic Defence Review, Britain's Harrier fleet is to be retired. Therefore, Illustrious will no longer launch any fixed wing fighter aircraft.". The reference (BBC News) says that the Navy will be unable to launch planes from aircraft carriers until 2019. As I understand it, the plan is that a new fleet(?) of aircraft will be eventually be built to replace the Harriers, so as long as they don't start the second Falklands War for ten years, it should be okay. --Kateshortforbob _talk 11:47, 5 November 2010 (UTC)

(edit conflict)HMS Illustrious (R06)#2010 says (citing Janes) that the Harriers themselves will be retired. Military of the Falkland Islands#Royal Air Force notes that the Falklands are defended by four Typhoons; that doesn't sound like a lot, but it's proportionately much more than defend the UK. -- Finlay McWalter ☻ Talk 11:50, 5 November 2010 (UTC)

Or decommissioning doesn't mean outright scrapping? Like, in case of some extreme emergency other solutions could be found, like investing more resources to reactivate them or complete the new models sooner, or just lease some from other countries? --131.188.3.20 (talk) 11:57, 5 November 2010 (UTC)

I would guess they also have ground defences, no? Nil Einne (talk) 12:04, 5 November 2010 (UTC)

Yes; there's a Rapier missile battery, an infantry company (rotated every 6 weeks) and support units[4]. Alansplodge (talk) 18:49, 5 November 2010 (UTC)

If they really wanted, they could probably buy the USS John F Kennedy which the US is finished with. Googlemeister (talk) 12:59, 5 November 2010 (UTC)

Using what for money? Lend-lease? Edison (talk) 16:09, 5 November 2010 (UTC)

Well the UK does own about something like $300 billion of US government debt... Googlemeister (talk) 18:18, 5 November 2010 (UTC)

In the next few years, all they will need will be something to lauch drones (Unmanned aerial vehicles) from, and helicopters. 92.15.10.141 (talk) 13:34, 5 November 2010 (UTC)

Could the four UK fighters based in the Falklands be expected to defeat the 41 combat aircraft and 24 ground attack aircraft of Argentina listed at Argentine Air Force ? Edison (talk) 16:09, 5 November 2010 (UTC)

The 4 Typhoons flew to the Falklands via Ascension Island with air-to-air refuelling[5]; therefore they could be reinforced at short notice by the same route. Several weeks of bombardment from air and sea failed to close ther runway at Stanley, so it should be possible to keep the new one open for a few days - excluding a successful amphibious assault. BTW in 1982 there were 28 Sea Harriers against 220 Argentinian combat aircraft - so rather better odds then than now. Alansplodge (talk) 17:16, 5 November 2010 (UTC)

The combat aircraft of the Argentine airforce are all designs that first flew between 40 and 50 years ago, and many have been small or downgraded platforms to begin with. Also, they probably have very limited supplies of modern ordnance. So I would not bet against the Typhoons, which are considered to be among the best current fighter aircraft. However, I also suspect that the risk of a rerun of the Falklands war is minuscule at the moment. --Stephan Schulz (talk) 17:33, 5 November 2010 (UTC)

But not inconcievable[6]. Alansplodge (talk) 19:10, 5 November 2010 (UTC)

Political posturing doesn't mean they have the capability to deliver military effect at range. One of the main issues that the Arg forces had during Corporate was the distance from base they were operating at, so their mission generation rate was quite low compared to the mission generation rate of the defending aircraft. Also time on target was very limited.

The level of threat to FI is negligible at the moment.

ALR (talk) 19:27, 5 November 2010 (UTC)

OK, but everyone in HMG thought the threat was negligible in 1981. Alansplodge (talk) 08:44, 6 November 2010 (UTC)

Even if Argentina do invade, is it likely they will commit their entire air force to the invasion? This seems a bad idea to me. According to Falklands War there were 75 aircraft of various types + 25 helicopters that time around. This is far less then the 220 quoted above. Argentine air forces in the Falklands War also seems to support the idea that Argentina did not deply their entire air force to the Falklands. In terms of the other point, it seems to me the nature of government in Argentina is quite different then from now. Nil Einne (talk) 09:44, 6 November 2010 (UTC)

The Argentine air forces in the Falklands War article says that about half were retained for defence against Chile. The list of units engaged gives 105 Air Force combat jets, of which 34 were lost, and 18 Navy jets with 5 lost. It also says that a lack of tanker aircraft was a limiting factor. Alansplodge (talk) 18:19, 6 November 2010 (UTC)

(edit conflict) The AAF is largely comprised of the same aircraft that badly lost the 1982 conflict; only the compliment of reconditioned USMC Lockheed Martin A-4AR Fightinghawks was acquired after that, and they're not very impressive. Argentina has been unable to acquire (and in fairness mostly unwilling to spend money on) F-16s or Mirage 2000s. In addition to the Typhoons, the Royal Navy routinely deploys an attack submarine submarine in the South Atlantic (example), armed (depending on mission) with spearfish torpedoes and TLAMs. -- Finlay McWalter ☻ Talk 17:59, 5 November 2010 (UTC)

Plus a standing patrol by a destroyer or frigate and an auxilliary called the Atlantic Patrol Task South, APT(S). Alansplodge (talk) 08:52, 6 November 2010 (UTC)

One would assume that the radar facilities on the Falklands are much better than they were in 1982. Not just for military purposes either, but to monitor the fishing industry that now provides much of the islands' income. Physchim62 (talk) 19:24, 5 November 2010 (UTC)

Different types of radar. Monitoring the while picture would be done using AIS as surface search has a very limited range. IN practice the fisheries industry is monitored by ships anyway. That's part of the role of HMS Clyde (P257).

ALR (talk) 19:30, 5 November 2010 (UTC)

The current Harrier capability is Ground Attack and Recce anyway, the aircraft aren't fighters and wouldn't be used as such. In practice all of the capabilities currently delivered by the Harriers could be delivered by UAVs using current technology.

ALR (talk) 19:27, 5 November 2010 (UTC)

Childhood

Why does childhood only last 18 years? jc iindyysgvxc (my contributions) 13:37, 5 November 2010 (UTC)

It doesn't. Maturity in humans doesn't end until the mid-20's. Then, after a period of stabilization, many humans go through a relapse into a second childhood. -- kainaw™ 14:16, 5 November 2010 (UTC)

Childhood is the age span ranging from birth to adolescence, typically between the ages 13 and 19. Biologically the development from child to adult is the process of Puberty whose onset is usually between 10-13, having dropped from an average 16.5 in England in 1840. A significantly Delayed puberty is regarded as an abnormality with an underlying cause that needs investigation and possibly correction by hormone treatment. Age 18 or a range of other ages are used in formal thresholds in laws that define Age of consent, Coming of age and in the age of reason rules for baptism in Western Christian churches. In many countries, there is an age of majority when childhood officially ends and a person legally becomes an adult. The age ranges anywhere from 13 to 21, with 18 just being the most common. Cuddlyable3 (talk) 14:25, 5 November 2010 (UTC)

I think kainaw's first two sentences refer to studies suggesting that brain development isn't complete until the early 20s. Comet Tuttle (talk) 17:43, 5 November 2010 (UTC)

This article discusses recent trends in extended child-like behaviour [7]. In short, the claim is the average twenty-something today doesn't really fit into classic 'child-adolescent-adult' classification schemes. SemanticMantis (talk) 14:53, 5 November 2010 (UTC)

Numerous US politicians have dismissed things they would prefer to forget as "youthful indiscretions." Several back as far as Bill Clinton said their use of drugs while in college was a "youthful indiscretion[8]." Unsuccessful Supreme Court nominee G. Harrold Carswell said his vow of "segregation forever" at age 27 was a "youthful indiscretion[9]." Bobby Kennedy serving as Counsel for Joseph McCarthy's redbaiting House committee at age 27 was dismissed later as a "youthful indiscretion[10]." George W. Bush said his drunk driving arrest at age 30 was a "youthful indiscretion". Grover Cleveland dismissed the fathering of a child out of wedlock when he was 37 as a youthful indiscretion [11], [12]. Vice President Dan Quayle, while a candidate said his vote against a Veteran's Administration cabinet position at age 41 was a "youthful indiscretion.[13]" Representative Henry Hyde said his five year affair with a married woman from age 41 to 45 was a "youthful indiscretion." Childhood among politicians thus may extend to 45. Edison (talk) 15:26, 5 November 2010 (UTC)

Brain development never really ends, as neuroplasticity occurs. See also developmental stage theories. ~AH1^(TCU) 17:42, 7 November 2010 (UTC)

Chemistry

CH3-CH=CH-CH2-CH3+HBr -> ? —Preceding unsigned comment added by 121.245.138.117 (talk) 13:46, 5 November 2010 (UTC)

Hbr#Uses_of_HBr may be useful, we don't do you homework though. SmartSE (talk) 14:20, 5 November 2010 (UTC)

Also Electrophilic addition, and even more specifically, Hydrohalogenation. Buddy431 (talk) 17:31, 5 November 2010 (UTC)

genetically modified foods

what are the most commmon genetic modifications to produce? 70.241.22.82 (talk) 13:56, 5 November 2010 (UTC)

According to this article: GMO corn (maize), GMO soy, rBGH milk, GMO canola (oil), and, interestingly, aspartame, which is produced these days using GMO bacteria. That sounds pretty plausible to me. --Mr.98 (talk) 14:04, 5 November 2010 (UTC)

If you were meaning what are the actual modifications that are made, the most common are resistance to glyphosate (a herbicide) and adding bt toxin (an insecticide). SmartSE (talk) 14:13, 5 November 2010 (UTC)

time constant for capacitor in both parallel and series

Suppose there is a resistor R1 after a battery, that then forks into a capacitor and a resistor R2 (that is they are both at the same potential difference). The circuit is then closed.

I am having a real hard time finding a succinct derivation of the time constant for this circuit. When t=0, most of the current (that is, E/R1) flows through the capacitor, but as time goes on, the current flows through R2 as the resistance of the capacitor becomes infinite.

How do I solve for the time constant? Neither google or the articles are helping me. John Riemann Soong (talk) 15:17, 5 November 2010 (UTC)

I don't get our explanation for charging a capacitor in parallel with a resistor. How does the time constant change in this case? John Riemann Soong (talk) 15:21, 5 November 2010 (UTC)

Mmmh fiddly. How far have you got:

1. If Q_t is the charge on the capacitor at time t (at time=0 charge=0)

2. The the voltage across the capacitor V_c is Q_t/C

3. The voltage across R₂ must be the same, they are in parallel (more on this later)

4. So the voltage across R1 is V-Q_t/C , and this voltage equals R₁I_t where I_t is the current through R1 at time t, (I_t is also the net current)

5. So I_c,t+I_r2,t=I_t (the currents through R2 and the capacitor equal the net current)

Also

6. I_r2,tR₂=V_c (see no. 3)

7. Therfor I_r2,t=Q_t/CR₂

8. So I_c,t+I_r2,t=I_c,t+Q_t/CR₂ , which equals I_t

9. Combining 8 and 4 gives:

(I_c,t+Q_t/CR₂)R₁=V-Q_t/C

But Q_t is got from the integral of I_c,t.dt (from 0 to t)

So 9 is a differential equation, and all that needs to be done is solve it.

Before that is attempted - did that make sense, are there any obvious mistakes in the above? (I haven't completed it)>94.72.205.11 (talk) 18:54, 5 November 2010 (UTC)

Wait what is the resistance of a capacitor as a function of time? Every time I look it up it says "resistance is infinite" but this is for a charged capacitor, not a capacitor that is charging. John Riemann Soong (talk) 19:09, 5 November 2010 (UTC)

If the charging voltage across a capacitor is greater than the voltage the capacitor is charged to then I would assume that the resistance of the capacitor is zero. (Have you tried the deriving the case when there isn't a R2 ie battery,resistor,capacitor ? - the current in that simpler case is (V_battery-V_capacitor)/R₁ eg not divided by R₁+R_c because R_c=0 ).19:28, 5 November 2010 (UTC)

Wait doesn't the resistance of the capacitor start at zero uncharged and increase to infinity when it's fully charged? I'm just trying to characterise the current division as a function of time. John Riemann Soong (talk) 19:44, 5 November 2010 (UTC)

(reply) that's what I just said -the resistance is zero until the capacitor is fully charged, at which point it becomes infinite.94.72.205.11 (talk) 20:12, 5 November 2010 (UTC)

How do I obtain a formula for the resistance of the capacitor as a function of time? John Riemann Soong (talk) 20:15, 5 November 2010 (UTC)

Welllll, That's actually simple - no need to solve - as you already noticed the resistance is zero until the capacitor is is fully charged. So the next question is "when is it fully charged" - hopefully it will be obvious that the capacitor never becomes fully charged - or to put it another way it becomes fully charged at t=infinity.

However if you want to calculate the 'effective resistance' (can't quite remember what that's called) - then all you need to do is solve the above equation - ie from step 9 onwards - to get the capacitor charge as a function of time, this gives you the capacitor voltage, the current through the capacitor is the rate of change of charge with respect to time, and the resitance (effective) is V/I not sure if that last bit is right nevertheless, with the solved equation for capacitor voltage and charge as a function of time you should have enough information to calculate simply any other parameters you desire... 94.72.205.11 (talk) 20:46, 5 November 2010 (UTC)

Imagine that you let your circuit charge the capacitor to equilibrium, and then set the battery voltage to zero. Assuming that your battery is an ideal voltage source, i.e. with an impedance of zero, then it will be equivalent to a short circuit. Your circuit then looks like a capacitor in parallel with two parallel resistors. Therefore the capacitor will discharge through R1||R2. So the time constant is 1/2π(R1||R2||C). If my life depended on it then I would use PSpice to verify my answer. --Heron (talk) 19:55, 5 November 2010 (UTC)

I don't get your derivation. Can you explain it to me? John Riemann Soong (talk) 20:10, 5 November 2010 (UTC)

Try the one I gave you ? 94.72.205.11 (talk) 20:13, 5 November 2010 (UTC)

Sorry. That was the formula for cutoff frequency, not time constant. I confused you needlessly there. I meant τ = (R1||R2)C. Does that make any more sense? I'm trying to avoid nasty differential equations by using a bit of lateral thinking. --Heron (talk) 20:32, 5 November 2010 (UTC)

Speaking of horrible differential equations, the above solution (9) appears to be of the form dx/dt=k+ax_t , where x is a function of t, x_t=0=0 dx_t/dt=k when t=0 , which possibly has a solution x=ke^ax-k (though as I mentioned before . I haven't checked the derivation) .. 94.72.205.11 (talk) 21:25, 5 November 2010 (UTC)

I get tau = R2+R1/(R2*R1*C). Does this seem correct? John Riemann Soong (talk) 21:36, 5 November 2010 (UTC)

I'm guessing you solved for ..e^{-tau x t}.. instead of ..e^{-t / tau} , as you answer is so close, if not how the hell did you get that?? :) 94.72.205.11 (talk) 23:07, 5 November 2010 (UTC)

No, dimensional analysis will tell you that that is wrong, but it works if you add a pair of parentheses around the first two terms and then turn the fraction upside-down. I just solved the circuit using Laplace transforms and it confirms my original guess: τ = (R1||R2)C. Translating that from electronics-speak into maths-speak:

$\tau ={{R_{1}R_{2}C} \over {R_{1}+R_{2}}}$

I had to refresh my knowledge of Laplace transforms from this very helpful lesson. Example 1 is almost the same as your problem, but you have to add another resistor. I'm leaving out a lot of details because it would take forever to type it all in Tex format, but I will supply as much information as you want on request. --Heron (talk) 22:29, 5 November 2010 (UTC)

question

If an airoplane was crashing, why don't people wait til it's a few feet from the ground and then just jump the short distance? —Preceding unsigned comment added by 85.140.85.64 (talk) 15:30, 5 November 2010 (UTC)

No, because you'd still be traveling towards the ground at hundreds of miles per hour. (You cannot possibly jump hard enough to even come close to counteracting that.)

You're better off in your seat, buckled in. Let the plane absorb as much of the impact as it can. (Of course, if the plane is just plummeting straight down, that won't save you either.) APL (talk) 15:43, 5 November 2010 (UTC)

And even if you could jump with enough force to counteract most of the speed you are going down with, you are going to hurt yourself with you hit the ceiling. And then there is the horizontal portion of your vector, so you will hit the front of the plane at high speed. Jumping is not a great way to avoid getting hurt here. Googlemeister (talk) 15:51, 5 November 2010 (UTC)

An ejection seat is your answer. It might even save a troll who could not jump very high. Edison (talk) 15:58, 5 November 2010 (UTC)

I had assumed he meant jumping out of the plane. (Wait until the plane is a foot from the ground and then jump! A one foot fall never hurt anyone! Sorry. Doesn't work like that. ) APL (talk) 16:08, 5 November 2010 (UTC)

Note that Mythbusters did an episode on a similar idea: jumping right before a free falling elevator crashed to the ground. - Akamad (talk) 16:34, 5 November 2010 (UTC)

I think that the OP meant to jump out of the airplane when it's a few feet off the ground; jumping a few feet wouldn't hurt you like falling a few hundred feet. --75.33.217.61 (talk) 16:55, 5 November 2010 (UTC)

1- Falling hurts because, by the time you hit the ground, you're going really really fast.

2- An airplane that has just fallen 40,000ft is going really really fast.

3- If you jump off something that is moving really really fast, you will hit the ground really really fast.

So yea, the speed you gain during that last foot won't hurt you, but it doesn't magically get rid of the speed you gained during the previous 39,999 feet. APL (talk) 17:00, 5 November 2010 (UTC)

To give a concrete example, suppose the plane is falling downward at 300 kph. You, also, are falling downward at 300 kph. When you're 1cm off the ground, you leap upward. Let's say your upward speed right at the fastest point of your jump is 20 kph. The net downward speed of your body is still 280 kph, which is enough to break your bones and rupture important organs like your heart, brain, and liver. Now, if you had some way to leap upward at a speed of about 300 kph, as in the ejector seat suggestion above, then your net speed would be 0 kph and you could land on your feet quite gently (though of course there are lots of airplane parts bouncing into you at a speed of 300 kph). Comet Tuttle (talk) 17:39, 5 November 2010 (UTC)

With one centimetre to spare and travelling at 300 km/h, an ejector seat would do exactly zip to save you: decelerating enough for the impact not to potentially kill you, in such a small time frame, would be lethal anyway. You would not land gently; using any real ejector seat, you'd crash almost exactly as hard as you would without, and using a hypothetical ejection seat that decelerates you to non-lethal velocity in 1 cm, you'd be pancaked against the seat. In other words, unless Scotty beams you up in those last few microseconds, you will go splat. --Link ^(t•c•m) 19:24, 5 November 2010 (UTC)

Agreed, sorry, I shouldn't have mentioned the ejector seat as being able to achieve my desired outcome. Comet Tuttle (talk) 20:35, 5 November 2010 (UTC)

That and most ejector seats have a minimum altitude and speed for effectiveness, since you usually need time for the canopy to clear. Googlemeister (talk) 19:42, 5 November 2010 (UTC)

A blanket claim that ejector seats don't work if the crashing plane is near the ground is refuted by many videos of successful ejections. If not "1 cm," then how about a few meters?Youtube At an air show, the pilot is likely to wait until the last second to make sure the plane does not crash into the crowd. Edison (talk) 22:22, 5 November 2010 (UTC)

Leaving the aircraft at the first sign of trouble as Vesna Vulović did, worked for her. From aircraft speeds, she just slowed down to her own terminal velocity. --Aspro (talk) 18:36, 5 November 2010 (UTC)

She's not alone - see Free fall#Surviving falls. Alansplodge (talk) 19:15, 5 November 2010 (UTC)

For better advice, though, see List of sole survivors of airline accidents or incidents. Comet Tuttle (talk) 20:35, 5 November 2010 (UTC)

In addition to all of the points made above, in order to get out of the plane you first need to get to an exit. --Anonymous, 00:20 UTC, November 6, 2010.

Springs question

In another discussion it was said that when a spring was compressed its mass increases by a tiny amount due to the stored energy. If this is true, why not have two springs, compress the first one, move the uncompressed one forward, compress that one, uncompress the other one and pull it to the compressed one and create a reaction-less drive? The force would be too tiny to be practical, but this is a thought experiment [Trevor Loughlin]80.1.88.13 (talk) 15:41, 5 November 2010 (UTC)

Because the energy that you're using to compress the springs ALSO has mass. (And the kinetic energy released when the spring decompresses!) APL (talk) 15:46, 5 November 2010 (UTC)

No energy enters or leaves the system, so it has a constant mass, and thus the ZMF is inertial. As expected. —Preceding unsigned comment added by 129.67.37.227 (talk) 16:08, 5 November 2010 (UTC)

Oscars eating chicken

I fed my oscars some shreds of raw chicken cutlet and I see them defecating what appears to be similar-sized, fully formed strips of the same cutlet -- can they not digest bird meat? Or is it that the cutlets are too tough, and, for instance, the beef heart that I buy at the pet store is ground first? Mind you my oscars are about 2 inches long. DRosenbach ^{(Talk | Contribs)} 19:25, 5 November 2010 (UTC)

Carnivorous fish (I think carnivorous animals in general) have poor digestive systems ie very short intestines (unlike the cow which has an advanced digestive system). I'm not surprised. Can't definitely say nothing is wrong though.94.72.205.11 (talk) 19:34, 5 November 2010 (UTC)

Here's some basic links http://www.aqualex.org/elearning/fish_feeding/english/digestion/fr_structure.html (the diagram says it all I think - basically the intestine of a carnivorous fish is nearly a straight pipe.

Also http://www.umaine.edu/aquaculture/GeneralInfo/Biology/Anatomy/digestion.htm "The length of the intestine is dependent upon the type of diet. Herbivorous fish often have intestines twenty times longer than their body length. Carnivorous fish, such as the cod, have an intestine length about equal to their body length." - the intestine just isn't long enough to significantly break down the food.94.72.205.11 (talk) 19:42, 5 November 2010 (UTC)

I'm not familiar with Oscars but for for the Walking catfish I can confirm what the first link above says - eg that they have a mouth, then an (expandable) stomach, and after that, basically nothing - just a short pipe to to anus. It's like having a stomach, but not large or small intestine..94.72.205.11 (talk) 19:47, 5 November 2010 (UTC)

Hairy dandelion

I saw in the UK something like a dandelion, except its leaves are not indented, and they are hairy on both sides. What could it be? Thanks 92.29.112.206 (talk) 20:40, 5 November 2010 (UTC)

My bet would be Cat's-ear (or Catsear) Hypochoeris radicata from the same Compositae family as the Dandelion. "The leaves of dandelions are jagged in appearance, whereas those of catsear are more lobe-shaped and hairy". My trusty Observer's Book of Wild Flowers (1937, revised 1963) says "Plentiful in meadows, pastures and waste places throughout the country" (ie the United Kingdom). The pictures in our article seem to be of a half-dead one, but there's a nice illustration here[14]. Alansplodge (talk) 09:16, 6 November 2010 (UTC)

The edges of the leaves are not indented but irregularly wavey. Not like the linked illustration, but more like the as you say half-dead Wikipedia photo. Thanks. 92.15.28.27 (talk) 14:45, 6 November 2010 (UTC)

I haven't made a study but in dandelions there is a great deal of irregularity in the leaf patterns; some have wholly unindented leaves while others are deeply incised almost to the stem. The catsear illustration itself seems to show several distinct leaf forms. The Observer's Book says; "a circlet of rough hairy leaves, their edges scalloped..." which agrees with your description. Alansplodge (talk) 17:36, 6 November 2010 (UTC)

Cherry thieves

During the late summer, I left the cherries on a dwarf cherry tree to ripen a little longer before I picked them. When I returned they had all disapeared, including the stalks, except for one half-eaten cherry that was still on its stalk. There were no fallen cherries below the tree.

If they were eaten by birds, is it usual for them to remove the stalks as well? Thanks. 92.29.112.206 (talk) 20:48, 5 November 2010 (UTC)

I had a cherry tree that I did not protect sufficiently well and a couple of blackbirds took the cherries and the stalks. PR - but every little helps. Richard Avery (talk) 22:53, 5 November 2010 (UTC)

AESA vs Active-cancellation

Given the current lack of FTL CPUs, isn't Active-cancellation (Thales Spectra) worse than useless against Active Electronically Scanned Array radars? It's like trying to use Noise-cancelling headphones against White noise. Hcobb (talk) 20:50, 5 November 2010 (UTC)

Active RADAR is not "white noise" - though they may be broad-band and may seem like "noise" to the "untrained eye." Pulse patterns are deterministic and depend on the hostile system's design. If an ELINT aircraft positively identifies RADAR type, it can configure its countermeasures to match expected returns. The ultimate objective in such electronic countermeasures is to know what signal the enemy RADAR expects to receive (as an echo)- which is both a SIGINT and a HUMINT challenge - and then to send something else (as a transmitted signal that looks like an echo). The active response system then sends a spoof response based on known parameters of the enemy RADAR. Of course, if the enemy RADAR uses counter-counter-electronic-countermeasures, your spoof response might indicate your presence or even give away your location. In some cases, "active-noise cancellation headphone" style methods would work: for example, if the enemy RADAR were using a CW illuminator (an archaic, but possible scenario), then you could phase-match and retransmit a deconstructively interfering signal to "null" your echo. Nimur (talk) 21:02, 5 November 2010 (UTC)

Horripilation

Is there any way to induce goosebumps? I am kind of fascinated by them but (or maybe because) to my knowledge I have never experienced them. I have been cold, I have felt awe, and I have felt creeped out—nada. It is possible I have piloerectile dysfunction?--141.155.159.142 (talk) 22:00, 5 November 2010 (UTC)

Apparently it is possible to induce goosebumps at will. [15]. Mitch Ames (talk) 05:56, 6 November 2010 (UTC)

More than two parents

Just watched the new BBC series 'First Life' (new Attenborough one started) and it got to the point where it stated that once animals sexually reproduced it vastly increased the genetic mutation / variations and therefore is considered a big factor in the speed of change of animal development. Anyhoo as with my electricity question a few days ago...it got me thinking. It seems to be pretty much standard that every new born animal is created by the 'dna' of 2 parents - a mum and a dad if you will. Are there any animals that are the offspring of more than 2 parents? (I.e. their DNA is made up of 3 animals rather than 2 or 1)? ny156uk (talk) 22:11, 5 November 2010 (UTC)

There's at least one case of a human (two humans, actually - twins) being conceived of the DNA content of their mother's egg and two of their fathers' sperm [16]. They are genetic mosaics, which means that each given cell bears the DNA of only two parental gametes, not all three. Theoretically speaking, if the mother had had sex with two different men in very close succession, she could have borne mosaic children with genetic contributions of three different people (herself and two fathers). However, it should be noted that even if this does ever occur in the animal kingdom, it is probably a rare event that has not been selected for by evolution. In any mammal, having more than two parents by such a mosaicism-producing mechanism is problematic because it can create infertile offspring that are male/female mosaics, as is the case in the paper I cite above. Someguy1221 (talk) 03:22, 6 November 2010 (UTC)

An article a few years ago in Discover mentioned an indigenous tribe in Colombia where it is the norm for the fetus to undergo "repeated washes of sperm" by a second father during the mother's pregnancy. ~AH1^(TCU) 17:32, 7 November 2010 (UTC)

Bdelloid_rotifers are very odd. They have essentially given up true sexual reproduction and no haploid eggs or males have ever been found. They can survive long periods of dessication, and, when `re-animating', they absorb and incorporate surrounding DNA. It is my understanding that three females could dry out and break to pieces, and one individual with genetic material from three distinct female `parents' could emerge. 74.98.22.146 (talk) 02:40, 9 November 2010 (UTC)

Is it true that all matter gives off at least some radiation?

Topic says it all. ScienceApe (talk) 22:16, 5 November 2010 (UTC)

I think so. I think that matter gives off some radiation from the vibration of atoms and molecules. The only way to stop matter from giving off radiation would be to cool it to absolute zero. --The High Fin Sperm Whale 22:25, 5 November 2010 (UTC)

Did you mean "radiation" as in radioactivity ? (I think the answer for real world stuff is still yes) eg carbon 14 is present in almost all life, similar weakly radioactive isotopes exist for a wide variety of elements, so most rocks etc will also be at least very slightly radioactive.

If you meant "radiation" as in electromagnetic spectrum the answer is still yes (in particular blackbody radiation), the emission stops at absolute zero (-273C), but that's impossible to reach.94.72.205.11 (talk) 22:53, 5 November 2010 (UTC)

You might be interested in our article on background radiation. Physchim62 (talk) 00:24, 6 November 2010 (UTC)

Thermal radiation. --Wrongfilter (talk) 08:58, 6 November 2010 (UTC)

Unknown mushrooms

Anyone know what these strange mushrooms are? Thanks, --The High Fin Sperm Whale 22:16, 5 November 2010 (UTC)

Narrow it down a bit - where did you find them? I don't recognize them, but I imagine the mushrooms growing in Central Europe (that I'm somewhat familiar with) differ from those growing in Britain or Asia or over the Pond in the American landmasses. TomorrowTime (talk) 06:50, 6 November 2010 (UTC)

User resides in British Columbia.--Shantavira|^{feed me} 12:38, 6 November 2010 (UTC)

1. just look at my userpage, 2. look at the coordinates on the picture. But if you want a bit more information, I found them beside a pile of old sticks and shrubs near the entrance to a forest. --The High Fin Sperm Whale 17:06, 6 November 2010 (UTC)

Well, I'm afraid I can't help you (I only know mushrooms as a hobby, and my knowledge is limited to ones I can find in my backwoods), but I hope someone else can. If that fails, maybe you could ask at a mushroom pickers' club or something near you? TomorrowTime (talk) 17:43, 7 November 2010 (UTC)

Try uploading it to Mushroom Observer, it's apparently the best place to get IDs. SmartSE (talk) 18:23, 7 November 2010 (UTC)

November 6

Lizard Salivation

It was a particularity cold day today, even though I live Southern Florida. I have a Cuban Anole, and knowing that lizards are cold blooded desided to warm him/her up by placinh him/her in some lukewarm water (I was sure the water was not to hot). I left him there to warm up a rock and on my return I found him, seemingly sleeping, but more important he was what seemed to be salivating a lot. My Concern: Is this normal? Should I be concerned? And how do I now if it is a boy or girl? 66.229.227.191 (talk) 01:30, 6 November 2010 (UTC)

First of all, as evident by our article on Cuban Anoles, there are two types. Assuming yours is a Brown anole, then see if it has a dewlap to determine the sex (males do, females do not). And was the anole touching the water? If so, when the water evaporated the anole would be cooled even more (in the same way sweat cools us). If it was asleep, then we know it was just getting cooler. I suppose the drooling occurred because when it was asleep, it didn't know it was drooling. And I don't think you should be concerned as long as the temperature was above 0° C; reptiles, as the temperature drops, simply get less and less conscious. However, below 0° C, they will die, because the ice will damage tissues. --The High Fin Sperm Whale 02:25, 6 November 2010 (UTC)

I've never heard a brown anole called a Cuban Anole... but yea, its a Cuban Knight Anole. I understand that water evaporates, but thats normally under wind shear and he was inside and completely emerged. That's strange, I've never seen him/her do that before, maybe

someone could elaborate more 66.229.227.191 (talk) 02:39, 6 November 2010 (UTC)

If it's a Cuban Knight Anole, then still see if it has a dewlap. Water evaporates all the time, albeit slowly. Even if not evaporated, the water would get as cold as the air around it after you took it out, so warming by using water is not a good idea, I would think. And if you're wondering about the drooling, then see my earlier comment. Hope this helps, --The High Fin Sperm Whale 03:27, 6 November 2010 (UTC)

IBold text thought this said "lizard salvation".

percent algae death

What percent of oceanic algae death is necessary to reduce the amount of atmospheric oxygen by 10% and is there a curve for the relationship between oxygen and algae? --96.252.213.127 (talk) 03:37, 6 November 2010 (UTC)

Question one: I am not sure, but the amount would be enough to kill most organisms in the ocean. And even if all of those instantly died for some reason, they would reproduce so fast that in no time the population would be back to normal. Right now, I think the problem is to many algae, not to few.

Question two: Yes. There is a strong relationship between algae and oxygen.

Hope this helps, --The High Fin Sperm Whale 05:35, 6 November 2010 (UTC)

NO. It does not answer my question for I know that there is also a strong relationship between how much oxygen is needed and how many humans are asleep in a coal mine from which they must be rescued. What I am looking for is the numerical correlation or curve between oxygen production and algae on the planet Earth. --96.252.213.127 (talk) 14:42, 6 November 2010 (UTC)

It would be very tricky to set up a model to estimate a curve for the relationship. As oxygen decreases, carbon dioxide increases (at least as long as there are animals breathing), and this encourages the growth of plants, but they probably wouldn't fully compensate for the loss of algae. There are just too many unknown variables to derive an accurate relationship or to predict where an equilibrium would be reached for a given percentage of algae death. The coal mine is much simpler to model if there are only miners there. Someone might be able to make a guess at an answer for you, but experts are unlikely to agree or to be accurate because they will have to make many assumptions about what factors to include in the model. Dbfirs 17:47, 6 November 2010 (UTC)

The curve is very complex and needs to account for all the positive and negative feedback that occurs. You could try modeling it as a differential equation, but I suspect it will be very complex. John Riemann Soong (talk) 21:14, 6 November 2010 (UTC)

This has not been indubitably proven, but measurements using a Secchi disk and satellite analysis showed that the oceanic plankton population declined by 40% in the last 60 years. Also look at oxygen synthesis. ~AH1^(TCU) 17:26, 7 November 2010 (UTC)

jeans

why do jeans feel different on the outside than the on the inside? insint it the same fabric —Preceding unsigned comment added by Kj650 (talk • contribs) 04:37, 6 November 2010 (UTC)

Jeans are made from denim, which is a type of fabric called twill. According to our article "Twill fabrics technically have a front and a back side", presumably because of the way they are woven (described in the article). The two sides are different: the technical face side (front) is usually more durable and attractive. Presumably (the article doesn't actually say) the material feels different on each side because of the asymmetric weave. Mitch Ames (talk) 05:51, 6 November 2010 (UTC)

how do u weave something that has 2 sides —Preceding unsigned comment added by Kj650 (talk • contribs) 08:01, 6 November 2010 (UTC)

How do you weave something that hasn't? --Stephan Schulz (talk) 09:56, 6 November 2010 (UTC)

Like this. Mitch Ames (talk) 12:15, 6 November 2010 (UTC)

I think he means "two sides that are different". Judging by the twill article, I'd say you'd need to know a bit about weaving to understand it... Vimescarrot (talk) 10:30, 6 November 2010 (UTC)

The front side of a twill should feel the same as the reverse side at right angles.

However jeans material will have had it's front surface treated differently, (confirmed by the presence of dye) - this will also affect the feel.94.72.205.11 (talk) 12:00, 6 November 2010 (UTC)

They won't necessarily be the same after rotation, even without differential treatment. On something like a 3/1 twill, one side will have mostly the warp fibers exposed, whereas the reverse will have the weft exposed. During weaving, there's different tension on the two, so the "lay" will be different. Examining a pair of jeans, this appears to be the case. The ones I looked at appeared to be a 2/1 twill, with the high-tension warp threads being prominent on the inside, and the lower tension weft threads prominent on the outside. This gives the inside a smoother, flatter texture than the outside. Although it doesn't appear to be the case on the pair I examined, different thread types can be used on the warp versus weft, accentuating the difference. -- 174.31.204.207 (talk) 17:25, 6 November 2010 (UTC)

that's right, good point. 94.72.205.11 (talk) 18:21, 6 November 2010 (UTC)

Geology abbreviation

While looking at a job application, in the job description it is mentioned: Grade: Band 7/6 (SO/HSO). What does this mean, and what other grades are there? Thanks in advance. --Danninja (talk) 07:11, 6 November 2010 (UTC)

These are (probably UK government) officer grades: Scientific Officer (SO); Higher Scientific Officer (HSO); Senior Scientific Officer (SSO)

According to this site, point 6 was £29,412 in August 2009, but you should check with the employer before assuming that this is correct because Medical Scientific Officers at point 6 on the Liverpool University scale are currently paid only £23,366, and if the employment is in India where there are also "SO" scales, then the remuneration will be completely different. Dbfirs 08:12, 6 November 2010 (UTC)

Coccyx decay rumor

If anyone searches about Coccyx decay, they will get many results on the top confirming this rumor without any scientific evidence:

"Coccyx tail is the only bone that doesn't decay after one's death"

Is there any scientific citation?--Email4mobile (talk) 09:57, 6 November 2010 (UTC)

What exactly does "after one's death" mean? 10 years? 100 years? 1000 years? There are many, many places all over the world where human remains from several thousand years ago have been excavated and many of them have most of their bones intact.[17] Just think logically about the "rumour", why is the coccyx any different from any other bones in the body? Correct, it's not. So why should it decay in a different way. Richard Avery (talk) 13:34, 6 November 2010 (UTC)

Schiller's experiment

Few days ago I posted this question on the Michelson–Morley experiment talk page, but will repeat here: I've read a related article and it was astonishing but I don't know if it were reliable to add it to Michelson–Morley_experiment article?--Email4mobile (talk) 10:08, 6 November 2010 (UTC)

What I find astonishing is not the article or the confirmation of the results, but the crank comments that follow. I'm not sure that this experiment really adds anything to a long-established result, but we could add a note that the result has recently been confirmed to at least one part in 10¹³. Dbfirs 11:38, 6 November 2010 (UTC)

health care

This request to diagnose the cause of a health problem has been removed. -- kainaw™ 14:35, 6 November 2010 (UTC)

sorry, but I just had to edit your comment. --Chemicalinterest (talk) 15:02, 6 November 2010 (UTC)

How is combustion sustained in a jet engine?

Compressed air flows through the combustion chamber of a jet engine at several hundred miles per hour or more. How do they keep the flame from being extinguished? Do they have some kind of heating element that continuously tries to restart combustion? --173.49.14.225 (talk) 11:59, 6 November 2010 (UTC)

No, they don't. It's not necessary. 76.123.74.93 (talk) 13:58, 6 November 2010 (UTC)

Once a jet engine (where "jet engine" means turbojet or turbofan, for now) is started, the ignition system is turned off (it's mostly just a ring of spark plugs). From then on the flame is sustained by (subsonic) deflagration - the burning mass of fuel/air in the rearward end of the combustion chamber thermally heats the non-burning fuel-air mixture forward of it, causing it to burn. This means there's a stable flame-front in the engine, which self-sustains the flame without an external source of ignition. This process is aided by the incoming stream already being highly pressurised (overall pressure ratio gives ratios > 10:1). A flame holder in the air path provides an eddy environment to maintain the position of the flame front. Note that if things go wrong with the supply of air, fuel, or with the pressurisation provided by the turbine spools, the engine can flame out and must be reignited. This all works because the speed of air through a turbine engine is subsonic (even on supersonic aircraft); deflagration only works in a subsonic medium. If you tried to inject supersonic air, the deflagration couldn't keep up, the fire-front wouldn't maintain its position at the flame holder, would be blown backward, and the engine would flame out. As for truly supersonic engines, I think a scramjet needs a continuous ignition source, and a pulse detonation engine relies on supersonic detonation rather than subsonic deflagration, and I think may need a reignition for each pulse. -- Finlay McWalter ☻ Talk 15:34, 6 November 2010 (UTC)

Finlay's description above about the flame-front is excellent. The flame is constantly in a state of dynamic equilibrium as the chemical combustion takes place, using up fuel and air, and new air and fuel rushes in. Part of the difficulty of designing a safe jet engine is to make sure that the flame front is stable - that is, it must not be "wiggling around" a whole lot, or changing the magnitude or rate of combustion. This requires careful design (and possibly using active control of fan speed, turbo speed, fuel injection rate, and so on). If the combustion starts to oscillate (i.e., the "wind blows the flame front back and forth"), the thrust, fuel consumption, and other parameters may also oscillate - and this is a bad thing for safe flight.

Regarding scramjets: my understanding (and I admit my understanding of supersonic flows is limited) is that in a scramjet, the velocities and pressures are sufficient for autoignition - in a sense, you're creating hypergolic propellant out of jet fuel and highly supersonic atmospheric air. This can only happen stably in special high-velocity conditions; that is why scramjets typically require some other propulsion system to boost the vehicle up to speed. Our scramjet theory section outlines some math for comparing the aerothermal heating due to kinetic energy of the airstream; in sufficiently fast streams, the kinetic energy is greater than the ignition activation energy (hence, autoignition). Nimur (talk) 03:39, 8 November 2010 (UTC)

Air traffic control system

I may be getting the details of the story wrong. I think it was in the early '90s when I read about a problem with the ATC system in the US. The system was described as antiquated and running on obsolete hardware. Procuring repair parts for the hardware was getting difficult. And attempt to develop a modern software replacement was unsuccessful. I don't know if and how the situation have improved since, or whether the problem persisted.

My questions:

1. Has the US replaced the old ATC system with something modern and maintainable?
2. Why couldn't the US just buy whatever ATC system the Europeans were using at the time? Did the Europeans have the same problem?

--173.49.14.225 (talk) 12:15, 6 November 2010 (UTC)

The Wikipedia article Air traffic control will be of interest. It notes that In 1999, U.S.A. controllers began use of the Standard Terminal Automation Replacement System, which included new displays and capabilities for approach control facilities. Cuddlyable3 (talk) 23:10, 6 November 2010 (UTC)

ATC is extremely conservative. Over here, in Germany, the replacement system for the Upper Airspace Control in Karlsruhe has been under development for 15 years, but is still not operational. Of course, when they designed it they made it future-proof by using a client/server structure. And by picking the most advanced microprocessor for all components - the Alpha 21264, instead of one of the obviously dying Intel CISC kludges. For the US, buying an ATC system in Europe is hard to imagine. The US aviation market is very much cornered by the big US suppliers - Boeing, Raytheon, Lockheed Martin, and a few others - due to pork barrel spending policies and protectionism. See Next Generation Air Transportation System for the current transition in the US and Single European Sky for the next generation ATC systems in Europe. --Stephan Schulz (talk) 00:41, 7 November 2010 (UTC)

Possible future need for faster than light communication

What is to be done theoretically if the mankind becomes advanced to such an extent, when communication between remote human colonies and objects would require a faster-than-light transmission of signals? 85.222.86.130 (talk) 12:38, 6 November 2010 (UTC)

Why would it be required? If humans have extensive colonies thorough many different stars, they will learn to live with the fact contact between these will take several or many years (depend on how far we're talking about) and you may be dead before people in the other colony receive your message (although if you personally don't want that and with the tech required to set up these colonies who knows what may be possible, e.g. uploading yourself to a computer, some sort of stasis, a relativity time dilation device or even simple advances allowing near biological immortality). Considering it will take even more years for people to travel between these, I see no reason why people will somehow be unable to live with that. It may be nicer to have the soft SF near instant communication but there's no reason we can't live with the real physical universe we live in. Nil Einne (talk) 13:01, 6 November 2010 (UTC)

As far as we know, FTL communication is impossible — just plain ruled out by physics which seems pretty solid at this point. So I think we can throw that one out the window unless physics is totally wrong in some important respects. (Which is always possible — the quantum world certainly is weird and often surprising, even at this late date — but you can't bet on it.) What you more likely get are colonies that aren't in communication. That either means you have a limit on colonization, or you have a limit on how "connected" you expect your colonies to be, when they can only communicate with each other every few decades or so. The world of Ender's Game (or, rather, the sequels to that particular book) discusses these issues in great detail, although largely in reference to what FTL communication (through the fictional ansible) lets you do that otherwise you would not be able to do, politically, especially if you have it in absence of FTL travel (which means, in one book, that if you want to send a military fleet to an unruly colony, it'll arrive only after a number of decades from the colony's reference frame). In any case it seems pretty clear that you couldn't have the same degree of power projection between colonized worlds that you do between different nations on Earth, and your political models would have to reflect this reality. --Mr.98 (talk) 13:08, 6 November 2010 (UTC)

Browsed the superluminal communication, thanks. 85.222.86.130 (talk) 15:30, 6 November 2010 (UTC)

This form of communication may necessitate the controlled use of wormholes, strings or via the folding of space. ~AH1^(TCU) 17:21, 7 November 2010 (UTC)

Or quantum devices that can violate causality. Googlemeister (talk) 15:15, 8 November 2010 (UTC)

Solstice dates change from one year to another

I am wondering why the dates for solstices and equinoxes change from one year to another.

I'm assuming it is because the sidereal year is 365.256363004 days and our calendar is 365 days (3 out of every 4 years).

If it is because of that discrepancy, could a calendar be devised in which it did not change? What elements would be required to accomplish this? -Joel (talk) 14:26, 6 November 2010 (UTC)

• One small point. Because the Earth's orbit precesses, the sidereal year is irrelevant; the relevant version of the year is the tropical year. This is a bit under 365.25 days, which is why leap days are sometimes skipped rather than extra ones being added. --Anonymous, 20:13 UTC, November 7, 2010.

The relationship between the earth orbit's and the earth's rotation would need to change to integers. It's a good plan. --jpgordon^{::==( o )} 14:34, 6 November 2010 (UTC)

By that do you mean that our numeric system would need to change? There's got to be an easier way... I'm not thinking we'd need to ditch leap-years or anything. Could not the placement of the leap-year prevent the solstice date change? Like, with leap years in 2000, 2004, 2008 it will change, but with leap years in 2003, 2007, 2011 it won't. (It's really hard for me to think about trying to answer my question.) -Joel (talk) 14:48, 6 November 2010 (UTC)

I think jpgordon's reply was a subtle of saying that nature is messy and won't conform to our strictures or constructions. In other words, the plan would only work if the time for the Earth to go around the sun was an exact whole number multiple of the length of a day. Since it's not, that 'perfect' calendar simply can't exist. Changing when leap years are would make no practical difference. --jjron (talk) 16:04, 6 November 2010 (UTC)

... and even the year is not a fixed length. Our calendar is based on the average time between vernal equinoxes, and this is not quite the same as the mean tropical year. If we ignored sunlight and all lived according to an artificial "day" (not exactly 24 hours, and varying slightly from season to season) then we could have a fixed calendar, but I don't think it would be popular except possibly with those who work night shifts. Dbfirs 16:56, 6 November 2010 (UTC)

A further point is that solstices and equinoxes are instantaneous events. This means that the date when they occur depends on your local time zone. Since time zones exist that are over 24 hours apart (in Kiribati and Samoa, for example), any particular moment in real time always occurs on at least two different dates by zone time, sometimes three. For example, the upcoming solstice is at 23:28 UTC; it will be on December 21 in the UK and the Americas, but on December 22 in Australia, Asia, and most of Europe and Africa.

It would be possible to arrange a calendar so that a particular solstice was always on the same date, say December 21, in a particular part of the world. Whereas now we have leap years mostly at 4-year intervals with a fixed sequence of 8-year intervals, it could be decreed that leap years would be assigned dynamically at mostly 4-year and occasionally 5-year intervals, whichever would produce the desired effect. (The Islamic calendar is attached to the phases of the moon in a similar dynamic fashion.) But because of the time zones, this would not work for other parts of the world. There would be always be countries where it was not always on December 21.

Likewise, the time between one solstice or equinox and the event is not an integer number of days. For example, from the solstice this past September to the equinox coming in December is 89.853 days (the exact amount varies from year to year). This means that even if the equinox was fixed on December 21, the solstice might vary between September 22 and 23, for example.

--Anonymous, 04:57 UTC, November 7, 2010.

Leap year, leap second and nuclear clock may also be relevant. ~AH1^(TCU) 17:14, 7 November 2010 (UTC)

I can't find any reliable information on it on-line, but Duncan Steel has published a theory that the hidden purpose of the Roanoke colony was to establish a settlement at longitude 77°W, where if the 33-year Jalali calendar were adopted, the equinox would always fall on the same date. This is a summary, but not a RS. --ColinFine (talk) 19:18, 7 November 2010 (UTC)

Work done by Ice-Skater

A skater's body has rotational inertia 4.2 kg m^2 with his fists held to his chest and 5.7 kg m^2 with his arms outstretched. The skater is twirling at 3.0 rev/s while holding a 2.5-kg weight in each outstretched hand; the weights are 76 cm from his rotation axis. Fine the work done by the skater pulling the weights to his chest.

I plan to find the work by subtracting initial kinetic energy (when his arms are outstretched) from the final KE (arms at chest). But I'm having trouble understanding the various rules regarding rotational/translational KE. Any help?199.94.68.201 (talk) 15:01, 6 November 2010 (UTC)

0. Cuddlyable3 (talk) 22:39, 6 November 2010 (UTC)

It's not zero, Cuds. Work is done pulling the weights into the body, increasing the kinetic energy. You have the right approach, Mr. 199.94. You want to find the final rotational speed using Conservation of Angular Momentum. Formulas can be found in that article, and Rotational energy. Buddy431 (talk) 02:40, 7 November 2010 (UTC)

What Happens if the gravitational force decreases?

Bold textItalic text I am very eager to know that what happen when the gravitational force is reduces? i know that the gravitational force is acting indirectly to keep the percentage of oxygen in air. if it start reducing will the percentage of oxygen will remain same or not? If that force is reduced what will be the reason for that? Waiting for the reply. —Preceding unsigned comment added by Yuvraja (talk • contribs) 15:05, 6 November 2010 (UTC)

Fear not. The gravitational force is not decreasing. See Gravity of Earth and Newton's law of universal gravitation. --jjron (talk) 15:35, 6 November 2010 (UTC)

Gravitational attraction is lowest at the outermost layer of Earth's atmosphere, the Exosphere which is mainly composed of hydrogen and helium. That might become the composition of the whole atmosphere if the Earth's gravity were somehow reduced, though that would not be the first abnormality we would notice. Cuddlyable3 (talk) 17:00, 6 November 2010 (UTC)

(edit conflict)No, it is not decreasing, the only way to do that would be to get rid of a huge amount of mass. One much more common (in space) way to loose oxygen is when a planet looses, or never has, a magnetic field. This causes the solar wind to blow away the atmosphere. --The High Fin Sperm Whale 17:04, 6 November 2010 (UTC)

It is decreasing because the mass of the planet is decreasing. Think of all those spaceships we released... --Chemicalinterest (talk) 18:59, 6 November 2010 (UTC)

True, but think of all the rocks that have hit us! --The High Fin Sperm Whale 20:35, 6 November 2010 (UTC)

But what about that matter we converted to pure energy through detonating a hydrogen bomb? Googlemeister (talk) 15:10, 8 November 2010 (UTC)

If the gravitational force were to "magically" decrease you would have a wide variety of effects. For example air pressure would be lower, more air would escape into space (but not oxygen specifically, it would be the regular mix of air). More interesting would be the effects on the orbits of the planets - the planets would suddenly be orbiting too fast, and will move to farther orbits. A more important effect would be on the sun. Unlike the Earth the sun is held together by gravity. Additionally the nuclear reactions are controlled by the density and pressure in the center of the sun. If gravity were lower the suns output would decrease, this would cool the sun, causing it to shrink, which increases the density and pressure. I'm not sure if the end result will be the same level of brightness or not. Ariel. (talk) 23:50, 6 November 2010 (UTC)

A reduction if gravitational force would require a reduction in mass of the Earth, the number of gravitons (theoretical particle) emitted or the gravitational constant. Gravity travels at the speed of light, so if the Earth and Sun both lost some gravity, the orbital effects would be felt some 8.5 minutes later. ~AH1^(TCU) 17:11, 7 November 2010 (UTC)

Velocity management

The question appears quite weird in terms of special relativity, but anyway. Is it possible to extract the cause of light speed and manage it so that it could be multiplied? For example we take the light speed-producing conditions and multiply them just like we are adding more fuel to intensify the fire. Something like speed power of two photons cross-added, yielding roughly 600,000 m/sec. 85.222.86.130 (talk) 15:49, 6 November 2010 (UTC)

No. See article. Cuddlyable3 (talk) 16:42, 6 November 2010 (UTC)

(ec) You are correct in saying that the question sounds weird. Even if we knew the "cause of light speed", it is unlikely that we could "manage it" in any multiplicative way. From a mathematical and scientific point of view, the whole concept sounds like gobbledegook. Are you writing a science fantasy story? Dbfirs 16:44, 6 November 2010 (UTC)

To a certain crude approximation, the "cause of light speed" is the absence of invariant mass. (The "speed of light" is a fundamental property of the universe, and isn't special to light in any way.) It's not meaningful to say that something is "twice as massless". Two times zero is still zero. -- 174.31.204.207 (talk) 17:07, 6 November 2010 (UTC)

Heating house - turn off when I leave the house?

My husband and I debate over what we should do when we leave the house for a couple of hours. Should we turn off the heat, lower it, or leave it as is? Obviously, if we leave the house for a week it would make sence to turn the heat way down. Likewise, if we leave the house for 5 minutes, we would leave it alone. There must be a physics formula to answer my question. I've asked my friends, who just give me their opinions. —Preceding unsigned comment added by 74.90.197.121 (talk) 20:27, 6 November 2010 (UTC)

Much depends on the house and the climate. There's no one-size-fits-all answer about the time interval that would be suitable, but most programmable thermostats use four blocks of time: morning (warm), work (cool), evening (warm) and night (cool). I'd say around four to six hours of absence would be a good guide, based on that precedent, unless your house gets cold really quickly (and is quick to warm up again). Acroterion _(talk) 20:36, 6 November 2010 (UTC)

(edit conflict) Lowering the temperature always reduces heat loss, but whether this is a saving depends on whether you then turn the heat higher when you return. If you don't do this, then there will always be a saving in turning the heat off, but obviously for five minutes the few cents or pennies of saving will seldom be worth the effort. The graph never crosses zero, so there is no "break-even" point unless you factor in the wear on the switch. You will always save money by turning the heat off (though beware of frost damage in extreme cold). Dbfirs 20:38, 6 November 2010 (UTC)

To rephrase what Dbfirs said, it's always worth it to turn off the heat - unless, when you turn it back on, the furnace runs at a higher temperature. Usually the furnace does not run at a higher temperature, except if you have a modulating boiler or a heat pump. Most furnaces are either on or off, with no in between, but modulating boilers can change fire, and heat pumps will turn on auxiliary heat. Ariel. (talk) 23:46, 6 November 2010 (UTC)

Even if the furnace runs at a higher temperature for a while, it will not cost more unless the thermostat fails to turn it off at the set room temperature. The extra cost would only occur if there is some over-run, raising the room temperature higher than normal. I cannot see circumstances in which this would occur only after switching off, but I'm not an expert on heating systems, so I'm just looking at the whole-house boundary with the environment to give a simple answer. Dbfirs 00:24, 7 November 2010 (UTC)

In a modulating boiler the water temperature is adjusted based on the heat necessary. Usually it measure the outdoor temperature and sets it that way, but if the boiler sees that the call for heat lasts for more then X minutes it raises the temperature. The thing is, the higher the water temperature the lower the efficiency. The range is about 85% (180 degree water) to 98% (110 degree). In my house I only need 180 degree water when it's -20f outside. Interestingly with a modulating boiler, the typical recommendation to install a digital setback thermostat can actually cost you more, because the boiler has to raise the water temperature in order to heat the house quickly enough in the morning. The poorer efficiency when this happen can eat away any savings. I would love hard data on this subject (so I know what to do with mine), but I have not found any. Ariel. (talk) 01:19, 7 November 2010 (UTC)

Ah, yes, I hadn't considered the lowering of boiler efficiency where more heat or wasted fuel pours out through the boiler exhaust. Do no manufacturers provide an optional temperature-limiting control? Dbfirs 08:17, 7 November 2010 (UTC)

It's complicated. Cast iron boilers must run at 180 or above or they will rust from the water condensing from the exhaust. It's the same with the chimney - if water condenses in it it will dissolve the bricks. And finally if the temperature is not high enough the exhaust will not rise out of the chimney. All boilers (and furnaces) that can run at lower temperatures have stainless steel or aluminium parts, and exhaust using a fan. If you ever come across the terms Class 1, 2, 3 or 4 chimney, that's what the difference is. Ariel. (talk) 19:14, 7 November 2010 (UTC)

You should turn it off. The boiler (or whatever you call it where you live) will stop using fuel. And, as heat loss is proportional to the difference in temperature, less heat will be lost when the temperature difference between your house and the environment is lower, as it cools. Imagine a leaking bath. Rather than keeping water running into it all the time to keep it topped up, you use less water if you just fill it when you need it. I'm curious as to what the folk-model of physics would be that would give a different answer. (Hmmmn, maybe measuring rate rather than quantity). 92.24.189.145 (talk) 11:29, 7 November 2010 (UTC)

Yes, that was my analysis, but Ariel pointed out certain (very limited) circumstances in which the inefficiency of some boilers causes them to produce less heat for a given cost when running at high temperatures. If they do this for a while at switch-on, then there might be some circumstances in which money (not heat) might be wasted by switching off. I suspect that this effect is small. Dbfirs 18:00, 7 November 2010 (UTC)

They are wasting heat - it's going up the chimney, and it's not just at switch on either, the water is running at a higher temperature during most of heat cycle, while if you just left it it could run for longer, but at a lower i.e. more efficient temperature. But, the practical effect may be small like you say, I wish I had hard data. Ariel. (talk) 19:14, 7 November 2010 (UTC)

Another way to reduce energy use would be to have the heater turned off throughout a certain time period during the night, so that the temperature in your house varies similarly to the daily outdoor temperature fluctuations, and less energy is needed to heat during the day. ~AH1^(TCU) 17:08, 7 November 2010 (UTC)

If you have a heat pump, you need to understand that it will take longer for it to get warm, as heat pumps operate on a low temperature differential compared to other heating systems; the air coming out of the register will be cooler than air from a gas furnace, so heat pump systems can end up "chasing" a set point if the set point is changed too often. Also, heat pumps and air conditioning systems generally incorporate delay timers to prevent damage to the compressor from frequent start-stop operations, which can cause high back-pressures in the refrigerant loop. Acroterion _(talk) 21:19, 7 November 2010 (UTC)

Moles

QI said that all pictures of animal moles are of dead moles, posed in the ground and fluffed up. Is this true? Is there not pictures of live moles? —Preceding unsigned comment added by 78.113.39.122 (talk) 20:45, 6 November 2010 (UTC)

The photographer needs an enormous amount of patience and luck to get a picture of a live mole. Moles spend at least 99% of their time underground. I occasionally see one above ground, but often moving fast, so difficult to photograph. I've never tried to take a picture of one, but I think I would be tempted to cheat. Dbfirs 21:43, 6 November 2010 (UTC)

People catch live moles on video [18] [19] [20]. I changed the title from "question" which is not informative. Cuddlyable3 (talk) 22:55, 6 November 2010 (UTC)

I got a video of me holding one once. It came out of the ground, so a grabbed it and kept it in my cage for a few days, during which time I got pictures and videos. --The High Fin Sperm Whale 23:31, 6 November 2010 (UTC)

Yes, it would be easier to take video footage than to obtain a high-quality picture with a manually adjusted camera. I suppose it would be much easier to catch a mole in action (the classic pose is just pushing up a molehill) using modern fast autofocus. The problem with moles is that one never quite knows where they are going to appear, so it is difficult to have the camera ready focused. I'm sure there are many pictures of live moles in existence, but I understand the psychology of using a dead mole to get a good photo of a "mole in action"! Dbfirs 00:16, 7 November 2010 (UTC)

Moles don't hang around for people to do this.Cuddlyable3 (talk) 19:51, 7 November 2010 (UTC)

Touching neutron star matter

The core of a neutron star is not well understood from what I heard, but it's mostly just neutrons right? If you were to take a mass the size of a baseball from the core and put it in outerspace, would it still maintain its immense density or would it kinda dissipate into a cloud of neutrons? I guess what I want to know is, is pressure causing it to be dense, or is it just an intrinsic property that the stuff has? Would touching it kill you? If so, why? Also since just a small amount of it is so massive, is it possible to arrange a bunch of them in a line in outerspace and climb them like a ladder even though they aren't touching each other? ScienceApe (talk) 21:05, 6 November 2010 (UTC)

I think it's kind of moot; you'd be dead before you could get close enough to a neutron star to touch the stuff, for I imagine many many reasons, but tidal forces will suffice if nothing else gets you first. Sci-fi writers sometimes like to imagine that you could hack off a piece of neutron degenerate matter separately from the gravitational field that squishes it together, but I believe that is not true. --Trovatore (talk) 21:08, 6 November 2010 (UTC)

Why not? ScienceApe (talk) 21:34, 6 November 2010 (UTC)

I'll leave it to a physicist to answer in more detail. But see the linked article, especially at the top, where it talks about the dominant contribution to the pressure coming from the Pauli Exclusion Principle. Stands to reason, though I certainly haven't worked out the equations, that if you take off that pressure, it all blows apart. --Trovatore (talk) 21:39, 6 November 2010 (UTC)

Neutron_star#Structure has a diagram of an expected structure and make up of a neutron star - also the text next to it has a description. In general pressure is required to maintain the structure.94.72.205.11 (talk) 22:40, 6 November 2010 (UTC)

Free neutrons have a half-life of about 15 minutes before they decay into hydrogen, or a proton and a neutron. The only reason that in a neutron the stuff stays neutrons is that in the crushing pressures there is simply not enough room to have atoms (remember, the nucleus is about 1/100,000 the diameter of an atom). They are squeezed until they merge, forming neutrons. And you couldn't touch the stuff; if you magically got a piece of it outer space it would instantly explode. --The High Fin Sperm Whale 23:29, 6 November 2010 (UTC)

I thought the neutron-star-ladder was kind of a neat idea, though, ScienceApe. In principle. It would probably be difficult to arrange everything in order to get the sequential gravity assist to work just right, though. WikiDao ☯ (talk) 01:18, 7 November 2010 (UTC)

A marshmellow dropped on a neutron star would release roughly the same amount of energy as 50 Hiroshima bombs. So you'd explode. ~AH1^(TCU) 17:05, 7 November 2010 (UTC)

A baseball has a radius of about 37 mm, and thus a volume of about 212 ml. Then, according to the density from the article, it contains about 1.39*10⁴¹ neutrons. A neutron has a mean lifetime of about 886 seconds (the half-life is that times log(2)), and therefore the neutron baseball will have 1.57*10³⁸ neutron decays per second. The decay energy is 0.78 MeV = 1.25*10^-13 J, resulting in 1.96*10²⁵ W of power radiated from the baseball. Some of it would be in harmless neutrinos, but the rest would be still enough to make sure that you evaporate faster than you can move your arm in order to touch it... and the energy released in one second would be hundreds of billions times as large as that from the nuclear weapon that detonated in Hiroshima. Icek (talk) 03:52, 8 November 2010 (UTC)

Of course, that's why you need to put it in a Slaver stasis field. --Trovatore (talk) 03:56, 8 November 2010 (UTC)

If the neutrons are packed cheek to jowl, how can the ones on the inside decay at all? The electrons would be packed in at nuclear density which would be a very very high energy state for them. Wouldn't just the neutrons at the surface (or very near it) decay? Hcobb (talk) 04:29, 8 November 2010 (UTC)

What, no Larry Niven fans here? Never mind heat, think gravity. A neutron weighs 1.67*10⁻²⁹ kg, so 1.39*10⁴¹ of them would weigh 2.32*10¹² kg. The Earth weighs 5.974*10²⁴ kg, or 2.57*10¹² times as much. Therefore things will be attracted with a force (more precisely, an acceleration) of 1 gee to the neutronium ball if they are at a distance of sqrt(1/2.57*10¹²) Earth radius from its center. That is 1/1,600,000 Earth radius, or (6,370,000/1,600,000) meters: or just under 4 m. Come within 1 m and it'll be 16 gees. At 1 foot, 170 gees. At the surface, well over 10,000 gees. Get close enough to the thing to touch it and it'll wrap you around itself in a thin layer, moments after its tidal force (the difference in gravity between a nearer and a more distant position) rips your body apart. --Anonymous, 08:15 UTC, November 8, 2010.

Good thing your opponent cheated in the coin-throwing game, then. --Trovatore (talk) 08:32, 8 November 2010 (UTC)

That's the one I had in mind! Still can't remember the title—not "Neutron Star", of course. Well remembered. --Anon, 21:10 UTC, November 8, 2010.

There is a Tide. --Trovatore (talk) 21:16, 8 November 2010 (UTC)

Thanks! --Anon, 23:34 UTC, November 8, 2010.

I think you'd be vaporized before that. By the way, your number for the neutron mass is wrong by 2 orders of magnitude, it's 1.67*10⁻²⁷ kg, and therefore the distance at which the gravitational acceleration is 1 g is about 40 meters, and at the surface it's more than 1 million g. Another process that competes with a nice explosion is - if you are on a planetary surface - that it would fall towards the center of the planet, there is no rock that is hard enough to prevent that. Icek (talk) 09:08, 8 November 2010 (UTC)

Dang! All that calculating and I copied the number wrong. Sorry about that. But at least it was an error in Niven's tradition. :-) --Anon, 21:10 UTC, November 8, 2010.

On the decay within the neutron ball: I am not totally sure, but I would think that due to the release of the pressure the neutrons would already move further apart: If the density from the article is correct, then the distance between neutrons on a cubic face-centered lattice (which has the highest density possible for a lattice) would be 1.29 fm. Taking the diameter of the ²³⁸U nucleus (from Atomic nucleus), dividing the volume by the number of nucleons and taking the third root suggests an average distance of about 1.95 fm between neighboring nucleons.
But if it is true that the decay happens only on the surface, then we still have 1.03*10²⁸ neutrons at the surface, or 1.45*10¹² W of power, or 348 tons of TNT equivalent per second. Maybe it would evaporate a nice hole in the ground while falling towards the center of the Earth (if the neutrons in the inside decay, I would expect the ball to come apart pretty quickly). Icek (talk) 09:08, 8 November 2010 (UTC)

Suicide

What causes people to consider suicide other than depression? The Utahraptor^Talk/_Contribs 21:51, 6 November 2010 (UTC)

Suicide#Causes - specifically see the social causes, but also read the whole article for idea, also Assisted suicide Voluntary euthanasia has some ideas too. —Preceding unsigned comment added by 94.72.205.11 (talk) 22:23, 6 November 2010 (UTC)

See suicidal ideation and parasuicide. Often it's the sense of hitting a "dead end" in someone's life, even if that dead end is illusory. ~AH1^(TCU) 17:04, 7 November 2010 (UTC)

In some traditional societies it was expected as a matter of honour after certain failures. See Seppuku -- Q Chris (talk) 14:19, 8 November 2010 (UTC)

November 7

Beyond us

Are the problems in the world simply beyond us? Poverty, AIDS, human rights abuses, war. I am just wondering if that is what people learn as they try to accomplish things with a futility. Perhaps this should go in the misc section, but I was thinking that science should have the answer, above all things, right? AdbMonkey (talk) 00:22, 7 November 2010 (UTC)

It remains to be seen, AdbMonkey. We are awaiting the empirical results on that. Your last question reminds me of something I heard on NPR the other day, I'll see if I can dig that up for you in a moment... WikiDao ☯ (talk) 00:38, 7 November 2010 (UTC)

All you mention are problems we ourselves have created. The real question is, do we have the will to undo them? Perhaps we should start with renaming everyone's "defense" department back to their "department of war." Unfortunately, from war to pharmaceuticals, all is driven by the quest for profits. Unless of course you're just power hungry. Not to mention that the last "politician" I can think of where that moniker was not a dirty word was (for me in the U.S.) Hubert Humphrey. PЄTЄRS J VЄСRUМВА ►TALK 01:56, 7 November 2010 (UTC)

(e/c) Okay, that was a discussion on "Science and Morality" with Steven Pinker, Sam Harris,Simon Blackburn, and Lawrence Krauss. The lead-in to the program is:

"Did we evolve our sense of right and wrong, just like our opposable thumbs? Could scientific research ever turn up new facts to resolve sticky moral arguments such as euthanasia, or gay marriage? In this hour of Science Friday, we'll talk with philosophers and scientists about the origins of human values. Our guests are participating in an international conference entitled “The Origins of Morality: Evolution, Neuroscience and Their Implications (if Any) for Normative Ethics and Meta-ethics” being held in Tempe, Arizona on November 5-7. Listen in to their debate, and share your thoughts."

So far, I have only heard about the first 15 minutes of the program myself. But it may be relevant. If so, I'll comment further after having listened to the rest of it. :) Regards, WikiDao ☯ (talk) 02:10, 7 November 2010 (UTC)

To the OP: Not at all. Instead of comparing the current world to an ideal perfect world, without any form of suffering, instead compare today's world to that of say 50 years ago. Or 100 years ago. Or 200 years ago. Or 1000 years ago. At any point in history any arbitrarily long distance in the past, there were a higher proportion of people who were abjectly poor, or diseased, or who died young, or any other number of miserable existences. We've known about AIDS for about 30 years. Smallpox and Plague we knew about for centuries before they were finally cured. Give it time. It only seems like things are bad because you are living through them. Things were infinitely shittier before you were born. --Jayron32 03:23, 7 November 2010 (UTC)

That's a good point, and a good way of putting it. But, Jayron, the world is today in arguably a fundamentally different position than at any previous time with regard to humanity and its impacts on itself (overpopulation, technology, etc) and the world in general (environmentally, etc). It's a complex system, and as it gets more complex it gets more difficult to tell what's going to happen next... WikiDao ☯ (talk) 03:47, 7 November 2010 (UTC)

I'm not so sure about that. Ever since people began living in cities, they have been creating problems for themselves that living in caves did not. As bad as pollution was at the height of the Industrial Revolution, it still didn't cause as much death and illness as something as plainly simple as not shitting in the middle of the street. Progress tends to, on the balance, result in a higher standard of living across the board. It is true that technology and advancement causes unique problems, but it solves more problems than it causes. Despite the problems with polution, the Industrial Revolution in the UK saw the greatest population explosion that country ever saw. And as the modern economy has evolved, polution has gotten better. Yes, it is still a problem, but not nearly the problem it was in the middle 1800s. Thomas Malthus's predictions haven't come true, because his assumption that food production growth would be linear doesn't hold up. Food production has kept up with population growth because of technological advancements. The only major problems with overpopulation are politically created; its not that the food doesn't exist to feed people, or that the technology doesn't exist to fix the problems of overpopulation, its just that the political will to actually fix the problems lags behind the technological advancements. But that has always been so, and what has also always been so is that it eventually catches up. --Jayron32 03:59, 7 November 2010 (UTC)

Okay, sure, and if it does work out for humanity (and we ought to find out within the next century or so -- if we get through the tail-end here of the population explosion that has gone hand-in-hand with technological and social progress, it'll happen or not within the next hundred years) – if it does work out, it will be because it is as you describe it. I take your points about cities and failed Malthusian expectations. Still, we are globally overpopulated now. It's a closed complex system, and we've run up against the boundaries. What happens in a petri-dish when the bacteria run out of nutrients and fill it with their waste-products...? WikiDao ☯ (talk) 04:16, 7 November 2010 (UTC)

Actually, technological and social progress tends to lead to LOWER population growth, not more. See Demographic-economic paradox, aka The Paradox of Prosperity. In highly developed nations, like most of Western Europe and North America, the birth rate is below replacement rate, and these nations have to import workers from less developed nations just to do all of the work that the kids they aren't having aren't doing. The real question is what is going to happen to the world when EVERY country is so developed that we're all operating at below replacement rate. The trend would indicate that we're going to have the OPPOSITE of a Malthusian catastrophe, in that as we become more advanced, we don't even have enough kids to maintain a steady population. --Jayron32 04:24, 7 November 2010 (UTC)

A sigmoid curve.

Human population growth.

Yes. We are aiming for something like the diagram (of a sigmoid curve) shown at the left. That region on the upper-right-hand side is the region we are just entering now (see the diagram on the right and the World Population article, which says, "In the 20th century, the world saw the biggest increase in its population in human history due to lessening of the mortality rate in many countries due to medical advances and massive increase in agricultural productivity attributed to the Green Revolution," which is one of the things I was saying, too). WikiDao ☯ (talk) 04:36, 7 November 2010 (UTC)

Ah, it's he or she of the very funny user page, again! Hi, User:AdbMonkey! You might like to have a look at The Revolution of Hope, by the sociologist Erich Fromm. In one of his books, The Sane Society, I think it was, he makes a case, based on sociological metrics like suicide rates, alcoholism incidence, etc. for the idea that current Western society is more screwed up than it ever has been before. I've never seen his numbers discussed anywhere else, but (as I recall, it's been ten or twenty years) he claims the occurrence of such signs of distress is astronomically higher than ever before in recorded history. He's of the opinion that our technological development has way, way outstripped our moral intelligence, that we're like toddlers who think we can use fire responsibly because we know how to start one. ( I agree with this assessment, FWIW; it seems obvious to me. ) Along that same line, Fromm points out that if something can be done with technology, then eventually it almost certainly will be done, by someone, somewhere in the world; in this way technology has it's own inertia that sweeps us all along without much conscious choice or deliberation about whether the changes it introduces are what we really want, how we really want to live on the Earth. This is no way to run a planet, in Fromm's view. ;-) Then, in The Revolution of Hope (subtitled, "Toward a humanized technology") he gives one part of his "prescription" for what ails us as a people. Good fun, his ideas stretch the intellect, imo. Best,  – OhioStandard (talk) 04:36, 7 November 2010 (UTC)

Take a look at Malthusian catastrophe, The World Without Us, tipping point (sociology), philosophy of war, transhumanism, evolution of evolution and neuroplasticity. ~AH1^(TCU) 17:02, 7 November 2010 (UTC)

Thanks WikiDao. I have listened to some lectures by Pinker before. I'm not sure how he would answer the question. Thanks Jayron, for your way to reframe how I look at the world. Ohiostandard, you kill me. I was really wondering if there perhaps is a large school of once do-gooders, who have simply become jaded with trying to effectuate positive change (please no questions of how do we define positive and negative). I was just wondering if perhaps there was an ascribed term to this besides just "went through a green phase" or "became jaded" or "grew up and realized how the world worked." I hope I am making sense? I'm think specifically of a young person who is excited and hopeful and eager to make a positive change in the world, or help build schools, or volunteer with Medicans sans Frontieres, but they get weighed down and burnt out after awhile, when they see that their efforts don't make the dent they were hoping for. I was just wondering if older people has any wisdom about this, or if anyone knew any books about how to prevent this feeling of hopelessness, if there was a psychological scientific name for this, or if simply falls into the realm of motivational speaking. I hope I am making sense. AdbMonkey (talk) 19:31, 7 November 2010 (UTC)

Creeping nihilism? I say the best way to deal with it is to just stare it down. (You have nothing to lose by the attempt, right?;) WikiDao ☯ (talk) 19:59, 7 November 2010 (UTC)

Dear Wikidao. Is that all it is? I thought nihilism was when an anarchist destroyed everything. I just thought maybe there was German term for this or something. I like you, wikidao. You're very dao about things, and that is so nice. Even your name is cute, because it has wiki and dao put together in it. Ok, well I know this isn't supposed to be socially jabbered up with public declarations or odes to other users, but I just couldn't help telling you how I like the cutseyness of your name. (If you meant it to come across like a strong, karate kicking ninja, I apologize.) So yeah, thanks for that NPR link AdbMonkey (talk) 04:34, 8 November 2010 (UTC)

Well I'm flattered and all, I'm sure, monkey, but this really is not the place - I'll respond more to all that on your talk page. :)

So nihilism isn't really what you were describing? I realize the word has an "anarchist" feel to it, but didn't mean to suggest that aspect of it. And I wasn't really sure, just guessing (note the question mark there, after "Creeping nihilism?"). You don't mean just "disillusionment", though, right? So you are thinking of a "German term", then? I'm sure there must be one, perhaps someone else will get it. Regards, WikiDao ☯ (talk) 05:07, 8 November 2010 (UTC)

magazine

can u buy famous older issues directly from playboy? —Preceding unsigned comment added by Kj650 (talk • contribs) 01:59, 7 November 2010 (UTC)

This is science? Anyway, the Playboy store only has some issues available from the 1980s forward, plus a reproduction of the Marilyn Monroe one. Clarityfiend (talk) 03:34, 7 November 2010 (UTC)

IIRC, Playboy's website has digitized versions of every issue ever produced, so you can at least access it if you pay the subscription fee. There are other magazines which offer free digital versions of their back issues. Sports Illustrated has a full collection of scanned issues (not just text, but full digital scans of every page of every magazine) going back to their first issue, and it is entirely free to browse. It's also fully text searchable. --Jayron32 04:28, 7 November 2010 (UTC)

Interesting. The Playboy Archive lets you [cough, cough] "read" 53 back issues for free. And Jayron is correct; apparently you can get digital versions for each decade.[21] Clarityfiend (talk) 04:57, 7 November 2010 (UTC)

pollution question

How much chemical does it take for the environment to be labeled as contaminated? Is it the same for every chemical? —Preceding unsigned comment added by 75.138.217.43 (talk) 02:04, 7 November 2010 (UTC)

It's different. I assume it's related to how toxic the chemical is, how well the environment can handle it, and how long it takes for it to be biodegraded. For example oil in the gulf is not as big a problem as it would be near alaska. The gulf has lots of mechanisms to deal with oil (bacteria, warmth, etc), alaska doesn't. Salt would not be a problem near the ocean, but would be near the great lakes. Ariel. (talk) 02:21, 7 November 2010 (UTC)

I do have to respond to this by saying that everything in the environment is made entirely of chemicals. So, it's obviously not the same for every chemical. I'm guessing our questioner is referring to chemicals widely regards as pollutants, and the same is true for them. ANother perspective is that what is good for some plants will be deadly for others. So, huge variation. HiLo48 (talk) 03:58, 7 November 2010 (UTC)

Electronics/Physics question about laptop power supplies

Hi, all. Can any electronics/physics guru tell me what's likely to happen if I plug a newish Gateway laptop into mains via an old AC/DC power converter "brick" that's from a (much earlier, monochrome screen) Gateway laptop?

Specs for the converter/brick that came with the new laptop are DC Output 19V, 3.42 Amps, according to a label affixed to it. There's also a symbol between the "Volts" number and the "Amps" number that consists of a short, horizontal line with a parallel dashed line (in three segments) positioned just below it. I presume this has to do with the polarity of the bayonet-style connection jack that plugs in to the laptop? That jack is also represented figuratively by the familiar "two concentric rings" graphic that shows that its "negative" pole is on the periphery/outside of the jack, with the "positive" pole located at the center. A label on the bottom of the new laptop also says 19 Volts and 3.42 Amps, btw. The old converter/brick has the same parallel lines symbol as the new one, but no "concentric rings" graphic, and a legend that says it's specified to deliver 19 Volts and just 2.64 Amps. This would seem to mean that the "new" power supply is capable of delivering 30% more current at 19 Volts than the "old" one can, also at 19 Volts, right?

So if I try this, is something likely to melt, and if so, what? The power supply? The computer? Or might everything still be within tolerance? I could try it with the laptop battery installed and fully charged, of course; would that be safer in case the power supply fries? And if this would be a really dumb thing to attempt, would it be sufficiently less dumb if I were to try running the new laptop only in some very low-power mode while connected to mains via the old converter/brick?

No penalty for informed guessing: I probably won't try this, regardless of the advice I get here. But I'll formally state that, as an adult, I alone am responsible for the consequences of my actions. That means I won't blame anyone else if I try this and it disrupts the fabric of the space-time continum, sets my house on fire, or worse, fries my computer. If anyone wants to explain the physics of what's likely to happen, I'd be interested to know that, too, since that's at least half my interest in asking this question. Thanks!  – OhioStandard (talk) 04:04, 7 November 2010 (UTC)

Well, we don't yet have a guideline against answering disrupting-the-fabric-of-the-space-time-continuum advice questions so... ;) The solid-and-dashed-line symbol is a well-known symbol for DC. The AC symbol is a sine wave. It is 99% likely that the polarity of your DC output hasn't changed (keep in mind that 83% of statistics are made up on the spot). It is very rare that the "shield" (outer-most parts) of a device/plug is NOT designed to be the ground/earth/negative terminal. As to what could happen if you plugged it in...it depends. If your old power supply has overload protection built-in it might switch itself off if you try to draw too much current. Or it might just run a bit hotter than normal. Or it might overheat, melt something internally and catch alight. Either way using a full battery would lessen the current draw when you plugged it in. Note that even though the power supply is rated for X amps, it doesn't mean that the laptop draws X amps. It is likely that the power supply is over-designed by at least 10% compared to the maximum laptop draw current. YMMV. Regards, Zunaid 05:44, 7 November 2010 (UTC)

Thanks, Zunaid! That's the word I was reaching for, "overdesigned". I was wondering if the old power supply might be sufficiently overdesigned to allow the swap; good word. The laptop itself does have a sticker affixed to it that says 19 V and 3.42 A, just like the power supply that shipped with it, but I understand that may not mean much. E.g. maybe it only draws that high a current when bluetooth power is on, there's three PC cards inserted, it's ethernet circuits are busy, the DVD writer is writing, etc. etc., i.e. when the computer is operating at maximum load.

But can you also give me some feeling for what would happen, in terms of the relevant physics equations, if such a state occurred when I was using the old (2.64 A) power supply? In terms, for example, of Ohm's Law? Voltage is fixed, right? So if you start adding "loads" (fire up the DVD burner, turn on wireless networking, etc.) that does what, increase the overall resistance? ( Can you tell I'm no prodigy re this stuff? ;-) If that's correct, then ... Well, then I'm out to sea, I'm afraid. But I have the vaguely formed idea that one of the three Ohm's Law variables will somehow become too extreme, and bad things might happen.

I guess besides just knowing I could damage hardware, I'm also trying to get some glimpse about how the dynamic interaction of those variables might change with increasing load, how different parts and subsystems (or even running software routines?) might be adversely affected when one of those variables deviates too far outside normal limits. I know there's no unified, simple answer for all cases like this, but am I at least thinking of this at all correctly? What, for example, would happen in an exagerated instance similar to this case. What if I hooked up my "19 V, 3.42 A" laptop to a "19 V, 0.5 A" power supply? Apart from the smoke billowing from the power supply or the hard drive spinning at one-third of its normal speed (just kidding), is there any way to know what would be going on re the variables of Ohm's Law? Any way, from just the relevant equations, to demonstrate on paper why doing so would be bad? I could hardly be more ignorant about electricity, I'm afraid, but I'd like to be able to understand, just from formulae, if possible, what happens when a device "wants" to draw more current than a power supply can deliver.  – OhioStandard (talk) 06:43, 7 November 2010 (UTC)

Modern power supplies are Switch-mode power supplies with circuitry much more complex than simple Ohm's-law calculations, but the article doesn't say how they behave under overload conditions. My instinct is that they will just reduce the output voltage (and overheat slightly rather than bursting into flame), but I haven't run any tests to confirm or refute this claim. I have successfully run a laptop with the wrong power supply, but not under serious overload, and I wouldn't recommend the practice. Dbfirs 07:59, 7 November 2010 (UTC)

The key terms here are internal resistance and electrical power, the power supply has internal resistance (like a battery does - see the article) - and the power dissapated (as heat) is V²/R or I²R. For this it's probably easier to use the equation with I (current, amps) - try to draw 3.42A from a 0.5A supply and you will be generating about 7 over 40 times as much heat - hence it gets hot - and possibly breaks. There's more detail and explanation on this if asked. using the V²/R equation is more complicated than it seems because the power supply switches on and off - in short V is not 19V, but a higher voltage in pulses

actually the relationship between current and heat given off in the power supply is not quite the same as the example above .. in fact the heat will be about proportional to the current for your example (because of the way SMPSs work) - which means about 7 times in the above example.Sf5xeplus (talk) 08:58, 7 November 2010 (UTC)

In practice the power supply will have some sort of overload protection built in (probably by law). I'm not so sure that it would reduce the voltage as suggested by dbfirs above, but it might. What I'd guess is that it either a. detects that the current is over the maximum rated (using a hall effect sensor) and/or detects when the device gets to hot (temperature sensor) - and then shuts off.

Note if the power supply is an old transformer (heavy) type the situation is a bit different.Sf5xeplus (talk) 08:24, 7 November 2010 (UTC)

Oh. - it's the power supply that is likely to melt, not the computer - though if the computer is run using a lower voltage than designed it may work, but there is an increasing likelyhood of the processor malfunctioning (not a permanent effect - just a crash as it freezes up or gets its sums wrong..)Sf5xeplus (talk) 08:47, 7 November 2010 (UTC)

You could well be correct about not reducing the voltage on overload. It was the old transformer-type supplies that behaved in that way. Surely someone has investigated the behaviour of modern supplies under overload? Do they just switch off? I haven't time to do the experiment just now. Dbfirs 10:30, 7 November 2010 (UTC)

Thanks, Dbfirs! Thanks Sf5xeplus! I appreciate your comments on this. So the likelihood seems to be that a modern power supply would probably have some variety of overlimit mechanism that would implement a non-catastrophic fail or suspension of current? Non-catastrophic to the connected computer, I mean, if not necessarily to the external power converter "brick" itself?  – OhioStandard (talk) 04:57, 8 November 2010 (UTC)

Cholera treatment

Somewhere several years ago I heard that Gatorade would be almost ideal for treatment of Cholera (presumably used for rehydration). I haven't been able to find anything to confirm this since, though, so how plausible of an idea is this? Ks0stm ^(T•C•G) 04:11, 7 November 2010 (UTC)

According to the article you link, in the lead " The severity of the diarrhea and vomiting can lead to rapid dehydration and electrolyte imbalance. Primary treatment is with oral or intravenous rehydration solutions." Presumably, in a pinch, Gatorade would work. From reading the article, it seems that the main problem with Cholera is the massive diarrhea and vomiting causes such rapid dehydration and electrolyte problems that that can kill you before your body has a chance to fight the infection. See also Oral rehydration therapy. --Jayron32 04:20, 7 November 2010 (UTC)

Well my main question rephrased was basically whether Gatorade (or Powerade, etc) would be effective for oral rehydration when stricken with Cholera, due to such drinks having the water, salt, and electrolytes needed to replenish those lost during the infection, or if there is something that would prevent their overall effectiveness as a treatment. I already read the articles in question searching to see if it mentioned anything about such drinks, but didn't see anything. Ks0stm ^(T•C•G) 04:31, 7 November 2010 (UTC)

I had a long, speculative post written out, then I did the google search. Gatorade was first proposed as a Cholera treatment in 1969 in the New England Journal of Medicine, and you don't get a better reliable source than that. See this. You could also find a wealth of information at this google search or this similar one. --Jayron32 04:44, 7 November 2010 (UTC)

Sodium secretion into the intestinal tract during a diarrheal illness is much greater than the typical losses you would expect in sweat from exercise. While sports drinks are fine for short-term replacement of fluid and electrolyte losses from sweating, the main reason you don't see those drinks being used widely for oral rehydration is that they simply don't have enough electrolytes to replace the severe losses from diarrheal illnesses. --- Medical geneticist (talk) 13:54, 7 November 2010 (UTC)

Sports drinks are also more expensive to store and transport than the little packets of oral rehydration salts. I doubt there's much Gatorade in Haiti at the moment! Physchim62 (talk) 19:24, 7 November 2010 (UTC)

Is the age of the universe relative?

Thanksverymuch (talk) 04:31, 7 November 2010 (UTC)

You'll want to read the articles Age of the universe and Comoving distance and Proper frame. The quoted age of the universe is the age given for the earth's current frame of reference, extrapolated back to the point of the Big Bang. In other words, we assume the age of the Universe to be for the Earth's current frame of reference (relative speed and location). We assume the earth to be stationary (what is called the "proper frame") and make all measurments assuming that. In reality, nothing is stationary. In a different reference frame (i.e. if you were moving at a different speed than the earth is), the age would of course be different. This is due to the issues raised by special relativity and general relativity. --Jayron32 04:37, 7 November 2010 (UTC)

Thanks! What is the maximum possible relative age of the universe? Thanksverymuch (talk) 04:46, 7 November 2010 (UTC)

That's impossible to answer, because of the way that time works. There is no universal reference frame for which we can measure against; there is no absolute time. There are an infinite number of reference frames which one could conceive of in which the universe could be literally any age. We choose the earth's reference frame because that's the one we're in. This is not the same thing as saying that the Universe is infinite in age, its just that we could arbitrarily choose any reference frame in which the Universe could be any age. --Jayron32 04:53, 7 November 2010 (UTC)

For an object moving at (over very close to) the speed of light since the big bang, how old is another object moving at the slowest possible speed since the big bang? Thanksverymuch (talk) 05:01, 7 November 2010 (UTC)

For an object moving at the speed of light relative to what? --Jayron32 05:02, 7 November 2010 (UTC)

A stationary object. Thanksverymuch (talk) 05:09, 7 November 2010 (UTC)

Stationary relative to what? --Jayron32 05:10, 7 November 2010 (UTC)

Let me ask the question differently - is there a reference frame that entails an infinitely old universe? If not, just how old can the universe get? Thanksverymuch (talk) 05:20, 7 November 2010 (UTC)

There is no reference frame that entails an infinitely old universe. There are an infinite number of reference frames that entail an arbitrarily old universe. There is a distinction between infinite and arbitrarily large. In every reference frame, the universe is a finite age. But as the number of possible reference frames is boundless, for any age you could pick, there is a reference frame for which the universe is THAT age. Does that make sense? --Jayron32 05:23, 7 November 2010 (UTC)

I was unaware of this distinction. It does make sense. Thanksverymuch (talk) 05:40, 7 November 2010 (UTC)

Actually, I was a little incorrect. The age of the universe is quoted not to Earth's reference frame, but to the reference frame of the Hubble flow, that is to the metric expansion of space. The universe is 13ish billion years old on that time frame. --Jayron32 05:30, 7 November 2010 (UTC)

Thanks for the clarification. Thanksverymuch (talk) 05:40, 7 November 2010 (UTC)

I wander though, are there really an infinite number of reference frames? Are there an infinite number of speeds? Are there an infinite number of gravitational states? If the number of reference frames is finite, it may be possible to calculate an upper and low bound for the age of the universe, and even an average age. Thoughts? Thanksverymuch (talk) 13:47, 7 November 2010 (UTC)

See multiverse, Milky Way#Velocity and cutoff. ~AH1^(TCU) 16:55, 7 November 2010 (UTC)

Jayron, are you sure that "for any age you could pick, there is a reference frame for which the universe is THAT age"? My knowledge of general relativity is somewhat sketchy, but surely in special relativity it makes sense to ask what the "maximum time" between two events is? There is always a frame in which the time between events is arbitrarily small, the observer's speed simpy has to be arbitrarily close to c. But at least in special relativity this doesn't work the other way around, and you can't find a frame in which the time between two events is arbitrarily large. What would the velocity of such a frame be? 213.49.88.236 (talk) 17:16, 7 November 2010 (UTC)

Yes, Jayron is incorrect about that; the usual quoted age of the universe is the maximum elapsed time from the big bang (and see this section for an explanation of what "big bang" means in this context). Also, the whole idea of using "reference frames" at cosmological scales is dubious. I don't like reference frames even in special relativity—I think they just interfere with understanding what the theory is about. But at least the term has an unambiguous meaning in special relativity. In general relativity it doesn't. -- BenRG (talk) 19:04, 7 November 2010 (UTC)

Now I'm lost. Is the age of universe relative or not? Thanksverymuch (talk) 19:52, 7 November 2010 (UTC)

The measured age of the universe does indeed depend on how the age of the universe is measured. However, ignore everything else from above, and let's start from scratch. Imagine a bunch of little clocks that were created all over the universe shortly after the big bang. The clocks are basically running stopwatches, which are created with their time starting off at zero. At the time of their creation, the clocks are scattered every which way, with their initial velocities all completely independent of each other. Fast forward to now, when a bunch of those clocks are collected, and examined in a laboratory on Earth.

There's a kind of radiation called the cosmic microwave background radiation, that was created all over the universe a few hundred thousand years after the big bang, and which is still detectable today. If you're traveling at roughly the right velocity (which the Earth is pretty close to), that radiation looks very close to the same no matter which direction you look in. Consider a clock that’s been at that right velocity for essentially its whole life (call it a "comoving" clock), that's also spent essentially its whole life far away from any galaxies or any other kind of object. A clock like that will say that it's been ticking for roughly 13.7 billion years.

None of the other clocks collected will read a time more than that (roughly) 13.7 billion years, but some of them will read less. In particular, clocks that have spent a big chunk of their life moving very fast relative to nearby comoving clocks will read less time due to time dilation due to relative velocity, a phenomenon which can be described as "moving clocks run slow." In addition, clocks that have spent a big chunk of their life close to a massive body will read less time due to gravitational time dilation, i.e., due to the massive body bending spacetime in that area. In either case, the clocks running slow has nothing to do with how the clocks operate, but is purely a matter of how time works.

None of the clocks will show precisely zero elapsed time, but the time shown on the clocks could in principle be an arbitrarily small positive number. In practice, clocks couldn't be completely stopped due to time dilation due to relative velocity, because it'd take an infinite amount of energy to try to get the clock up to moving at the speed of light. And clocks couldn't be completely stopped due to gravitational time dilation, because that would require them to be at the center of a black hole, from which you wouldn't be able to retrieve the clock, and which the clock wouldn't survive, anyway.

The clocks could show any amount of elapsed time in between close to zero and the roughly 13.7 billion years, so there are an infinite number of different amounts of elapsed times that the clocks could show, because there are an infinite number of different real numbers within any finite range of real numbers. But the size of the range of possible different values on the clocks is about 13.7 billion years, which of course is a finite amount of time. Red Act (talk) 09:47, 8 November 2010 (UTC)

Thanks for this excellent clarification Red Act! So the answer is a definite YES - The age of the universe is relative.

But this is not what is stated in the article on the age of the universe (I quote the lead paragraph - emphasis is mine):

The estimated age of the universe is 13.75 ± 0.17 billion years,[1] the time since the Big Bang. The uncertainty range has been obtained by the agreement of a number of scientific research projects. These projects included background radiation measurements and more ways to measure the expansion of the universe. Background radiation measurements give the cooling time of the universe since the Big Bang. Expansion of the universe measurements give accurate data to calculate the age of the universe.

Thanksverymuch (talk) 12:33, 8 November 2010 (UTC)

Not sure where you are going with this. In general relativity the time measured by a clock or an observer between two events - known, somewhat confusingly, as the proper time interval - depends not just on the events themselves but also on the motion of the clock/observer between the two events. So the time measured by a hypothetical clock/observer between the events that we label "Big Bang" and "now on Earth" will depend on the space-time path that the clock/observer took between those two events. If that dependency is what you mean by "relative" then the answer is yes, the age of the universe is "relative" - but, in that sense, so is any other measured proper time interval. How old are you ? Well, that depends on what path you have taken through space-time between the events "your birth" and "here and now" - see twin paradox. There is another measure of time, called coordinate time, that depends only on the space-time co-ordinates of the events themselves - and when the age of the universe is calculated as a coordinate time interval, it is about 13.7 billion years. But putting this qualification into the opening paragraph of age of the universe would make it needlessly complicated. Gandalf61 (talk) 13:21, 8 November 2010 (UTC)

Also note that some "clocks" could have experienced less time between the "big bang" and "now on earth", than the mentioned 13.7 billion years, there are no possible clocks which could have experience (significantly) more time than that. This is basically, because, the 13.7 billion years has been measured along a trajectory which is approximately geodesic, and (timelike) geodesics (locally) maximize proper time.TimothyRias (talk) 15:02, 8 November 2010 (UTC)

Um, it's way too general to say that "when the age of the universe is calculated as a coordinate time interval, it is about 13.7 billion years". That's not necessarily the case at all; depending on what coordinate system you use, the coordinate time for the age of the universe could basically be anything. I think comoving coordinates are almost always used when doing cosmology, but that's not automatically implied by the phrase "coordinate time", especially when dealing with a question about the different ways that the age of the universe might be measured. A statement that would be accurate would be "when the age of the universe is calculated as a comoving time interval, it is about 13.7 billion years". That's basically what I called a "comoving clock" in my simplified explanation above.

Thanksverymuch has a good point that it's not well explained in the age of the universe article as to how the 13.7 billion years is to be measured. The second paragraph says "13.73 years of cosmological time," but unfortunately cosmological time just redirects to Timeline of the Big Bang, rather than being an article about what is meant by the phrase "cosmological time". At least the Timeline of the Big Bang article does have a sentence near the beginning that says that the "cosmological time parameter of comoving coordinates" is used, so at least there's a description of comoving time within two clicks of the age of the universe article. Red Act (talk) 18:11, 8 November 2010 (UTC)

To Thanksverymuch: Your last statement makes it sound (to me) like you were playing a game of "gotcha". I do not appreciate that. On the off chance that you are serious, let me say that a free-falling massive particle which emerged from the Big Bang and arrived here and now would almost certainly have experienced a duration of about 13.75 billion years. So this is not relative in that sense. JRSpriggs (talk) 02:30, 9 November 2010 (UTC)

People meddling in the environment

Hearing a story about geoengineering on the radio today got me wondering if other attempts by people to "fix" the environment/Earth/ecosystems/etc have ever worked. (I'm open to various definitions of whether something can be said to have "worked" or not) What I was wondering about specifically was when we've introduced non-native species to an area to improve something. So, has this ever worked? Dismas|^(talk) 04:44, 7 November 2010 (UTC)

http://alic.arid.arizona.edu/invasive/sub2/p7.shtml Thanksverymuch (talk) 04:53, 7 November 2010 (UTC)

One famous example from Australia involved the introduction of the prickly pear cactus sometime in the 1800s, for some dopey reason, I think they were trying to use them as 'natural' fences or something. Anyway, they took off and were basically out of control, taking over swathes of the countryside with this impenetrable cactus thicket. In the 1920s the Cactoblastis cactorum cactus moth was introduced from South America and very quickly brought the prickly pear under control, almost wiping it out (there is still some around but it's not really a biological problem). This is a textbook case study of biological control in Australia as it was so successful in controlling the prickly pear and yet has had no known negative impacts on the environment. I see this is briefly described at Prickly_Pear#Ecology, and is also mentioned in the Cactoblastis article, where it notes that due to this success Cactoblastis was introduced elsewhere and has not always had the same benign impact. --jjron (talk) 11:51, 7 November 2010 (UTC)

Geoengineering is typically a very dangerous process involving the alteration of a complex hollistic global system, within which there are many unknowns and uncertainties. Introducing an alien species that may turn out to be invasive can be quite problematic, as can be sending sulfur dioxide droplets to the upper atmosphere to quell the tropospheric warming effect, since small abberations in controlling the climate by two-way forcing presents the risk of sudden abrupt climate change. Some schemes that may work include carbon dioxide air capture, but large-scale changes to the landscape or other environments can create many unintended consequences such as the theoretical phenomenon of too many wind farms causing an overall reduction in global average wind speed[22]. ~AH1^(TCU) 16:51, 7 November 2010 (UTC)

There are far more examples that worked than the other way. For instance, the environment I'm in right now is an artificial building designed to stop rain, help regulate air temperature, and even provide power. It has been very successful in this. There are also various areas that have been modified to farm food. Our current population would be impossible without these. I think most of human history can be described as humans modifying our environment. — DanielLC 01:34, 9 November 2010 (UTC)

Living donor liver transplant multiple times?

After a living living donor liver transplant, both the donor and recipient should eventually have a full-sized liver each. If it is required sometime in the future, could the donor or recipient be a living donor again? Has this happened before? thanks F (talk) 08:32, 7 November 2010 (UTC)

I'll happily be corrected but I don't think you could donate more than once. When you donate part of your liver, you give the recipient a large proportion of your right lobe (around 50-70%). Your left lobe then compensates by growing to make up the size lost. Anatomically speaking, however, you still only have a left lobe and a small portion of right lobe, so you won't be able to give that same 50-70% again. Besides all this, liver donation is a large, lengthy operation that lasts several hours. There's a large potential for infection and complications, so God knows why you'd want to go through the process twice! Regards, --—Cyclonenim | Chat  14:12, 7 November 2010 (UTC)

Also, when multiple people are involved in a liver transplant process, it's usually the first healthy donor who takes the longest to recover. ~AH1^(TCU) 16:42, 7 November 2010 (UTC)

Though the donor's remaining liver tissue does hypertrophy post-donation, it does not fully regenerate the original vascular structures; rather, the remaining vasculature serves the remaining (hypertrophied) liver. Because the vascular supply to (and drainage from) the donated liver tissue is crucial to the success of the graft in the recipient (PMID 12818839 and PMID 15371614 and PMID 17325920, the latter being particularly relevant), I think it's safe to surmise that a second donation would not be possible, even if the problem of perihepatic scarring from the first procedure could be overcome. Certainly, it's unlikely we'll ever have a study to support such a practice. -- Scray (talk) 21:15, 7 November 2010 (UTC)

Capacitor plague

Capacitor plague explains the problem, and repeats (what seems to be the common claim) that certain taiwanese manufacturers were to blame (due to using an incomplete electrolyte formula stolen from elsewhere..) - eg as repeated here [23] [24]

None of this I question; my question is: what about the fallout - ie what happened to the suppliers (eg I tried to find references to show that the manufacturers got their 'ass sued off' by the manufactures who bought from them) - but found nothing. As a side question - are compensation lawsuits uncommon in the far east? (sorry this isn't actually a science question - it's a science topic though..)

Also confusingly this Dell [25] page blames Nichicon, whereas the the other link says Nichicon was amongst those ".inundated with orders for low-ESR aluminum capacitors, as more customers shy away from Taiwanese-produced parts" ?. 94.72.205.11 (talk) 10:15, 7 November 2010 (UTC)

Since the OP complained Nil Einne (talk) 02:12, 8 November 2010 (UTC)

Well as you said, they used an incomplete electrolyte formula stolen from elsewhere. Given that happened in the first place, how likely is it they got their ass sued off by people who bought from them? Nil Einne (talk) 10:24, 7 November 2010 (UTC) I don't understand what you are saying - why is it not right to assume the buyer would sue or start criminal proceedings against them?94.72.205.11 (talk) 10:27, 7 November 2010 (UTC) I'm saying you can get an idea of the culture there by what caused the problem in the first place. This wasn't an isolated thing but quite a number of companies all producing the same crap from an incomplete stolen formula. It's also not likely the buyers were completely blind as to what's going on. (Super cheap capacitors don't suddenly appear from no where and I would expect many had their own quality control testing the stuff too, obviously not enough to pick up the flaws.) They obviously didn't expect capacitor plague but big companies have a fair idea of what they're getting in to (if they didn't they wouldn't be big companies). It's a risk they choose to take... In this particular case it came out badly for them. (Often it does not.) There may be some form of compensation but some of the companies undoutedly would have disappeared. There were likely some lawsuits involved as well. But ultimately the people who run the companies clearly didn't think much of using a stolen formula which they apparently didn't understand well enough to know was incomplete and flawed. Clearly they didn't consider the risks, say of being sued say by the people who designed that formula, high enough to outweigh the likely advantage they would gain from producing capacitors from the stolen formula. So it's not that surprising that the buyers themselves may not gain that much from whatever lawsuits did occur. In other words, ultimately I think it's quite likely the buyers bore the brunt of the cost. (Which as I've said, they must have anticipated when they went in.) Nil Einne (talk) 10:45, 7 November 2010 (UTC) The companies affected were at least two steps up in the supply chain, I'd also assume that the motherboard manufacturers wouldn't have bought components they new were going to fail on mass within a few months. That aside I was asking for factual answers, not your opinion. Can you please refrain from answering if you have nothing to offer but your own opinion.94.72.205.11 (talk) 14:11, 7 November 2010 (UTC) Well the first flaw in your statement is the components often didn't fail with a few months. In fact as our articles note one or two years is when problems start to appear. Also I don't know who said motherboard manufacturers would have bought components they knew were going to fail, I definitely didn't and made this clear. (Although I would note this was a fairly well known problem by 2003 [26] or earlier but our article suggests some equipment was still using faulty capacitors manufactured in 2007 and also [27] from the article is perhaps englightening. My impression from sources such as [28] is that there are actually still some crappy capacitors being used in new products to this very day although nowdays it's may perhaps be simply lower quality capacitors rather then the 'likely to fail way to soon' the historic ones appeared to be and there's also of course the continual problem of counterfeits.) I also don't know how you know the precise relationship between the many companies affected and the manufacturers, it isn't mentioned in our article and such things usually vary and are often fairly complex besides. The earlier ref BTW also mentions some affects on one manufacturer in terms of loss of orders (although I thought this went without saying). However the number of nominal manufacturers is huge, e.g. [29] and most involved on all sides probably have no desire for people to know precisely who knew what and did what and who compensated who. And how much so other then bits and pieces of that sort, the situation is likely to remain murky because the people involved want it that way so you're not likely to find a detailed writeup or refs. Nil Einne (talk) 00:11, 8 November 2010 (UTC) BTW, about the Nichicon thing, it appears correct that Nichicon had a batch or a few batches of bad caps. Their problems appear to have begun in 2003 [30]. This was after people had begun to avoid capacitors from Taiwan but to avoid speculation which you don't want, I'll just say the phrases 'increased demand' (well you yourself mentioned they were inundated with orders) and 'quality control problems when trying to meet increased demand' and let people speculate for themselves whether these phrases may be relevant. Several sources suggest the Nichicon capacitor problem may have been related to overfilling [31] [32] although some have expressed doubts [33]. (Overfilling does of course sound better then plenty of other execuses.) It's worth remembering that faulty components and manufacturing defects (and simply poorer quality components) are fairly common in this world. There were clearly some major problems early in this century according a few sources due to a stolen formula (since you want to avoid speculation I think we need to be clear we don't know for sure this is what happened, we only have clear cut evidence for know why the components were defective not how they got to be that way). However as is often the case everything tends to get swept up into the same boat so now any sign of capacitors failing are now automatically connected to the earlier problems. Nil Einne (talk) 01:13, 8 November 2010 (UTC) [34] non referenced, opinion based answer moved to editors talk page 94.72.205.11 (talk) 14:18, 7 November 2010 (UTC) I have restored the comments. Removing others' replies in this manner, particularly when they're entirely in good faith, is utterly unacceptable. -- Finlay McWalter ☻ Talk 15:56, 7 November 2010 (UTC)

Aeroplane crash

I read a question on here about jumping before a plane crashes to save you. obviously that wouldnt work, but what if you flooded the cabin with some sort of liquid or foam to spread the force acrost the entire body, and also provide more time to stop (reducing the accl, and thus the force). going from 300 km/h to zero over the distance of a few cm would be fatal, but over a couple of meters, it would be the equivilent force of going from 3 km/h to zero over a few cm. Would that work? 98.20.222.97 (talk) 10:03, 7 November 2010 (UTC)

or the cabin seats could be on a track that lets them slide forward a bit, making the stopping distance for the people inside greater —Preceding unsigned comment added by 98.20.222.97 (talk) 10:04, 7 November 2010 (UTC)

In theory, yes, but it is very difficult to find materials that will provide a gradual deceleration. To some extent, the crumpling of the metal of the plane already does this. Air bags are probably the most effective for the human body. Dbfirs 10:24, 7 November 2010 (UTC)

And there's a limit to the tradeoff between increasing safety, the real risks involved and other factors of practicality. Fitting each seat with a five-point racing harness and surrounding it with a roll cage should also increase the chance of survival, but at considerable other costs, both financial and other. Industries undertake substantial cost-benefit analyses on these things. The fact also remains that when dropping out of the sky from several kilometres up, sometimes nothing's going to save you. --jjron (talk) 11:38, 7 November 2010 (UTC)

Safety devices can cause risk also. One of the causes of the ValuJet Flight 592 crash was that it was transporting old oxygen generators, which are used to provide air to passengers in the event of pressure loss. Paul (Stansifer) 13:10, 7 November 2010 (UTC)

This is a famous article from The Economist which discusses some of the safety considerations in commercial air travel. Note that it was published in 2006, and so is out of date on a couple of points... Physchim62 (talk) 13:32, 7 November 2010 (UTC)

I think the best method would be to make every seat into an ejector seat with parachute, and to ensure all passengers always wear a life jacket in case the plane needs to eject passengers over water. Unfortunately, this system is not economical at all, and thus it will never happen for commercial airliners. Regards, --—Cyclonenim | Chat  14:04, 7 November 2010 (UTC)

The ejector seat idea is patently absurd. First, no commercial airliners are designed to have ejection seats. Fighter aircraft that have ejections seats have specially designed canopies that are blown off the airplane, or completely shattered a fraction of a second before the ejector rockets fire. I don't see how you can do anything remotely similar on a commercial airliner because the passengers have aluminum aircraft skin, overhead luggage storage and the like in the way. Second, people have to be specially trained to properly use an ejection seat. It requires preparation to eject since if you have an arm or leg sticking out when you eject, you are going to break bones, lose the limb, or even fail to eject properly. Another problem is how are you going to have a one size fits all ejection solution? What works for a standard sized person probably will not work well for a young child or the overweight guy sitting in the two seats next to you. Finally, even properly trained pilots are frequently seriously injured when they eject. Googlemeister (talk) 14:50, 8 November 2010 (UTC)

Your description of a crash sounds very similar to US Airways Flight 1549, in which the pilot successfully crash-landed on water without loss of life. ~AH1^(TCU) 16:40, 7 November 2010 (UTC)

It's worth keeping in mind that the number of people who die in airplane crashes is almost statistically insignificant, compared to the number who die in automobile crashes, a place where we have far more control over individual conditions, the speeds are generally a lot slower, and the obvious impact on society is much greater. We fear airplane crashes more because we perceive ourselves to have less control over their outcome (we are strapped into a pressurized tube going 500 km/hr at 20,000 ft), but car crashes are far more deadly. Far more people die per decade in Los Angeles from car accidents than do from earthquakes, yet people always fear quakes more than cars. People here seem to be very concerned about air travel as being not very safe, when in reality it is pretty safe and secure by comparison to more mundane means of getting around. --Mr.98 (talk) 16:56, 7 November 2010 (UTC)

One very simple step which would reduce risk would be to have all seats facing backwards. Unfortuantely, not marketable. HiLo48 (talk) 08:32, 8 November 2010 (UTC)

Rear facing seats would be more acceptable if there was a dummy cockpit door at the back of the aeroplane and the in-flight movie was more interesting than looking out of the window. Cuddlyable3 (talk) 08:57, 8 November 2010 (UTC)

Looking out the window facing backwards is not a problem — I've done that on trains; it's just as pretty as looking forwards. I don't think I'd be happy about being pressed into my seatbelt on takeoff. On the other hand, with the current arrangement, it happens on landing, so I'm not sure there's any net difference. --Trovatore (talk) 09:06, 8 November 2010 (UTC)

Risks of psych experiments involving rewards

You know how they let children paint on their own, then reward them for painting, and the children stop painting in the next trial? Isn't there a risk that a future painter, say, has been taken away from a life in the arts because of such experiments? Imagine Reason (talk) 14:33, 7 November 2010 (UTC)

Well I don't know the experiment in question you are referring to, but all experiments involving human subjects generally have to pass through an Institutional review board evaluation in the US, which looks quite closely to see whether or not there is real projected harm. In this case, you'd need to actually run the experiment many times to establish what long and short term effects there were before you decided that the experiment itself was harmful. If it were known as a iron rule that such experiments would discourage creative activity then they would probably be stopped. But I doubt it is as much of an iron rule as that. And on the scale of IRB concerns, "may in a very subtle way discourage a child from being interested in painting" probably ranks low on the "harm" list, especially since you have no way of knowing whether that child would have gone into a "life in the arts" anyway in the absence of said experiment. If there was an experiment that would, without much doubt, make it so that whomever it was performed on would never again do anything artistic (e.g., by removing that part of their brain or by use of negative conditioning or whatever), I am sure it would be deemed unethical. But this sounds like something far more subtle than that. --Mr.98 (talk) 16:49, 7 November 2010 (UTC)

ec(OR) Uh, no I don't know that children generally react as you describe. Competitions continually produce creative work and are a form of art patronage. They encourage artists by validating their artwork and expose them to their peers' works. Nobody has a right to a "life in the arts" unless they are prepared to earn it by contributing their work and talent. Sorry but to call rewarding a child for painting (whether you mean a picture or a fence) a "psych experiment" seems ridiculous, and the idea that it has deprived the world of painters is an unfalsifiable speculation. It would be nice if it worked on taggers. Cuddlyable3 (talk) 16:51, 7 November 2010 (UTC)

The scenario you describe, OP, is just plain un-Skinnerian. ;) I have never heard of such an experiment giving such results, and I believe there are many which have given the opposite result. retracted after comments that follow (Giving small "rewards" is usually considered ethical for the purposes of most psych experiments; proposing small punishments would probably at least prompt more careful review by the ethics board...). WikiDao ☯ (talk) 17:45, 7 November 2010 (UTC)

I've seen those experiments, where offering a reward leads to the activity not being valued in its own right, but rather for the reward. Children rewarded for drawing, and then given an unrewarded choice between drawing and another activity, will choose the other activity, whereas children unrewarded for drawing and given the choice will pick without apparently being influenced. It becomes work instead of play, and so isn't chosen for play. The studies I've seen have been brief, and wouldn't be expected to have lasting results: they will be swamped by all the other things they do, and all the other rewards and punishments they experience outside this brief experience. Or so the ethics discussion would go. 86.166.42.171 (talk) 22:22, 7 November 2010 (UTC)

The classic experiment (and it really is a classic in psychology, here's what google books has) was done by Mark Lepper, David Greene, and Richard Nisbett in 1973. For Wikipedia, see overjustification effect. ---Sluzzelin talk 22:33, 7 November 2010 (UTC)

You might be interested in this episode of Freakonomics Radio (the stuff I'm talking about is right at the end ; it's probably faster to read the transcript than listen to the show). In it, Levitt uses rewards to incentivise his daughter, and discovers a three year old is far from Pavlov's dog. -- Finlay McWalter ☻ Talk 23:05, 7 November 2010 (UTC)

I think (in answer to the OP's question) the risk is real but the risk is small. But the risk is nevertheless real. I think Imagine Reason raises a real and valid concern. Bus stop (talk) 01:26, 8 November 2010 (UTC)

I am not sure the risk is real. Even in classical conditioning, there needs to be lots of reinforcement to maintain behavior modification over time. It isn't the sort of thing that you do once and flips a switch and never goes again. People aren't that brittle. If they were, we'd have noticed it in so many other areas of life first... --Mr.98 (talk) 01:32, 8 November 2010 (UTC)

I understand that. But what I would say is that it constitutes miseducation, when contrasted with the child to whom it is conveyed that art is a wholesome activity. The message conveyed by the giving of a small and relatively meaningless reward is that the intrinsic reward in the activity is even lower than that. A lot depends on context. The child with already a grounding in the notion that art is worthwhile will not view the small "reward" as a reflection on the art activity. The child for whom the art activity is a totally new experience is looking for his first clues as to how society regards this activity. In the absence of a clue that something of value lies within this activity, he is left with the clue that the value in the activity is the small, meaningless reward. This is discouragement, the opposite of fostering an interest in the art. I think it is slightly cruel to take children whose minds have no opinion of art and introduce a negative opinion at such an early and impressionable age. Bus stop (talk) 02:02, 8 November 2010 (UTC)

The google books link that Sluzzelin provided (thanks, Sluzzelin, I was too dismissive and misinterpretive of the question in my intitial response -- something to be avoided!) says:

"This decrement in interest persisted for at least a week beyond the initial experimental session." emphasis added

It does begin to sound like something maybe they shouldn't be meddling with at that age, doesn't it...? WikiDao ☯ (talk) 02:19, 8 November 2010 (UTC)

I believe this is cognitive dissonance. This is also like the study of the group that played an intentionally boring game for the purposes of the experiment, and then were rewarded afterwards with money. Another group was not rewarded with anything and they convinced themselves they played the game for fun. The group with money justified playing the game because of the money. Anyway, cognitive biases aside, I don't think a serious artist would care much for a reward or not, but just for the thrill of doing the art for art's sake. Perhaps children not so enthused with art would be less inclined to be artistic if they were rewarded, but there are many cases where a person is so transfixed with their 'passion' that rewards are overlooked and do not matter because the job is it's own reward to that person. AdbMonkey (talk) 04:52, 8 November 2010 (UTC)

I don't think this is cognitive dissonance. Concerning a "serious artist," I think the most common situation would be a mix of motivations—both monetary and a motivation concerning the pure pursuit that is involved in using materials and techniques to achieve an end product. Bus stop (talk) 18:22, 8 November 2010 (UTC)

ground water

most precipitation sinks below ground until it reaches a layer of what kind of rock? —Preceding unsigned comment added by 204.237.4.46 (talk) 16:47, 7 November 2010 (UTC)

Impervious. Cuddlyable3 (talk) 16:53, 7 November 2010 (UTC)

Bedrock. See also aquifer and drainage. ~AH1^(TCU) 18:48, 7 November 2010 (UTC)

Unplugging mobile phone chargers

My new Nokia C5-00 phone tells me "unplug the charger from the socket to save energy" when I unplug the phone from the charger after charging. Will this really make a difference in regard of how much energy is consumed? I don't know much about electronics, but my general intuition tells me that a charger that is plugged into a socket but not actually plugged into any device does not form a closed circuit, where electricity would flow from a source to a destination, and so the electricity completely bypasses the charger, not adding to my electricity bill. Could someone who actually understands electronics clarify this? JIP | Talk 19:29, 7 November 2010 (UTC)

A charger or AC-to-DC converter draws a small current even when not delivering current and this is wasted energy that you may even feel as slight warmth from the case. I think your phone uses a switched-mode charger whose switching circuit works continually. In the case of a simple analog power supply, its mains input transformer takes a magnetising current. Some power may also go to light a LED indicator, if there is one on the charger. Wikipedia has an article about Battery charger. Cuddlyable3 (talk) 19:41, 7 November 2010 (UTC)

The no-load power drain is marginal, hardly registering on power meters, but I suppose it becomes significant if (like me) you leave lots of such chargers plugged in. The total drain is probably less than that of the transformer that runs my doorbell, but if everyone in the world did the same ... Dbfirs 00:22, 8 November 2010 (UTC)

(edit conflict)Do we have an article on phantom power? Nope, it doesn't go where I thought it would. Do however see standby power which goes over exactly what you're referring to. Dismas|^(talk) 00:24, 8 November 2010 (UTC)

Our article on Switched-mode power supply will also be of interest, but it doesn't state the no-load drain. Dbfirs 00:41, 8 November 2010 (UTC)

There's also the One Watt Initiative although perhaps not really relevant for mobile phone chargers where you probably want it much lower then that. Nil Einne (talk) 01:21, 8 November 2010 (UTC)

mitosis and meiosis

what are the formula used in mitosis and meiosis? —Preceding unsigned comment added by Oiram13 (talk • contribs) 22:58, 7 November 2010 (UTC)

I have no idea what sort of "formula" you are looking for. But to start you on your way to learning about these two processes, we have substantial articles about both mitosis and meiosis, including details about the numbers of chromosomes in each. DMacks (talk) 23:09, 7 November 2010 (UTC)

November 8

Fastest airship

For the greatest speed, would it be better to make a practical airship as large as possible, or as small as possible? 92.29.116.53 (talk) 01:06, 8 November 2010 (UTC)

I don't think it would be so much size as shape, and how smooth the edges are. For maximum speed, you would want to put the cabin inside. --The High Fin Sperm Whale 01:12, 8 November 2010 (UTC)

Our Airship article says:

"The disadvantages are that an airship has a very large reference area and comparatively large drag coefficient, thus a larger drag force compared to that of airplanes and even helicopters. Given the large flat plate area and wetted surface of an airship, a practical limit is reached around 80–100 miles per hour (130–160 km/h). Thus airships are used where speed is not critical."

Drag coefficient then says that "airships and some bodies of revolution use the volumetric drag coefficient, in which the reference area is the square of the cube root of the airship volume."

Clearly, all else being equal, a larger airship will have greater drag and will require greater thrust to maintain the same speed as a smaller airship. So you'd want a smaller airship for speed, down to the limit of no longer having enough lift to carry the same propulsion system (though you could probably get away with carrying less fuel, too, depending on your purposes). WikiDao ☯ (talk) 01:34, 8 November 2010 (UTC)

Given equal volumes and engine powers, a long thin airship can fly faster in still air than a short fat airship. Cuddlyable3 (talk) 08:44, 8 November 2010 (UTC)

While it's true that a smaller airship would have less drag, it would also only be able to support a smaller less powerful engine. The Zeppelins and similar airships were big things, they could have been built smaller. I'm unclear of the best ratio of power to drag, so the question is still open. I'm imagining an airship built to cross the Atlantic with the greatest speed, no expense spared. 92.15.3.137 (talk) 11:18, 8 November 2010 (UTC)

An airship would be able to cross the Atlantic from North America to Europe much faster then the reverse by using the jet stream, presuming your specific design was capable of high altitude flight. Googlemeister (talk) 14:38, 8 November 2010 (UTC)

Vaccinations of the Chilean miners

I'm curious about a line in the article about the Chilean mining accident saying the group was vaccinated against tetanus, diphtheria, flu, and pneumonia. Particularly flu and diphtheria; these diseases are caught from other people, and the group had already been isolated for three weeks by the time the vaccines were sent down, so if the diseases were present, wouldn't everyone have already been exposed? Or were the vaccinations a precautionary measure intended primarily for after the miners were rescued? Mathew5000 (talk) 02:10, 8 November 2010 (UTC)

It's common to use a DPT vaccine to immunize against both diptheria and tetanus at the same time, although exact protocols vary from country to country. Physchim62 (talk) 02:35, 8 November 2010 (UTC)

As for flu, it can be acquired through contact with a surface, and the miners were in contact with the "world above", including family members living in less than ideal conditions in Camp Esperanza. Physchim62 (talk) 02:41, 8 November 2010 (UTC)

Thanks. On the first point you're probably right although if they were given a DPT vaccine I'd expect news sources to mention all three diseases, whereas none of them mention pertussis. On the second point, I think you are correct again as I found a news article in Spanish [35] that explains, in connection with the vaccines, the concern about infection on the supplies they were sending down in the shaft, although they did apparently take “las precauciones de asepsia” before anything went down. Mathew5000 (talk) 07:36, 8 November 2010 (UTC)

You can get versions of the "DPT vaccine" that don't include the pertussus component, as is mentioned in our article, and (according to this report) these are the ones that are used for the maintenance vaccinations of adults in Chile (the triple DPT vaccine being given at age 2–6 months). The same report mentions that diptheria can be transmitted by "indirect contact with contaminated elements", although this is rare. So my guess is that the medical team were more worried about tetanus infection (an obvious risk for people working in a mine), and gave the DT vaccine either because that was the vaccine they were used to using in Chile or because they thought there was a potential risk of diptheria infection. Physchim62 (talk) 13:11, 8 November 2010 (UTC)

Thank you very much, Physchim62! —Mathew5000 (talk) 09:09, 9 November 2010 (UTC)

gravity

is gravity repulsive? —Preceding unsigned comment added by Ajay.v.k (talk • contribs) 03:32, 8 November 2010 (UTC)

Yes, I find it disgusting. How dare it not allow me to fly at will! HalfShadow 03:33, 8 November 2010 (UTC)

And have you even seen some of those equations that general relativity vomits out? Physchim62 (talk) 03:48, 8 November 2010 (UTC)

No, gravity always causes an attraction between two masses – it might be a very small attraction, but it is always an attraction, never a repulsion. Physchim62 (talk) 03:48, 8 November 2010 (UTC)

Unless you happen to have some Negative mass. DMacks (talk) 04:58, 8 November 2010 (UTC)

I just want to say, I think this is a very good question, because I was wondering what it would be like if the laws of gravity were reversed and if there was just a whole different way of looking at gravity. If gravity repeled for example. So anyway, OP if you could like, tell a little more about what got you to ask that question, I would be interested. AdbMonkey (talk) 04:59, 8 November 2010 (UTC)

The fact that gravity is an attraction only (and never a repulsion) makes it unlike the other fundamental forces. For this and other reasons, no quantum theory of gravity exists; and gravity can be described with general relativity (while other interactions like electrostatic force can not). Nimur (talk) 05:18, 8 November 2010 (UTC)

Is there a fundamental flaw in the theory that gravity is a repulsion between nothingness and masses? Cuddlyable3 (talk) 08:39, 8 November 2010 (UTC)

Some kinds of nothingness are very gravitationally attractive to masses. And I can't think of any kinds of nothingness that aren't – "nature abhors a vacuum". WikiDao ☯ (talk) 23:02, 8 November 2010 (UTC)

Black holes have a heck of a lot of somethingness. Red Act (talk) 23:53, 8 November 2010 (UTC)

General relativity doesn't even consider gravity to be an attraction. For example, the article on Newtonian gravity uses the word "attraction" 11 times, but the article on general relativity doesn't use it once. "Attraction" as used when discussing Newtonian gravity refers to a kind of action at a distance, which general relativity rejects. In reality, mass causes a curvature of spacetime in a purely local manner. Rather than being attracted to that distant massive object, other objects in that vicinity instead just travel along locally straight lines on that curved spacetime. When discussing the forces between particles, "attraction" can be a local phenomenon, in the form of an acceleration effected in a local manner via gauge bosons. But general relativity doesn't even consider gravity to be an acceleration, a complete theory of quantum gravity doesn't exist, and the gauge boson that would be involved in gravity, the graviton, has never been observed, so it's far from clear that that same form of "attraction" mechanism would also apply in any sense to gravity. Red Act (talk) 11:44, 8 November 2010 (UTC)

I just thought maybe there was some theory that a center point in the universe created the repulsion, so that gravity was actually repulsion, but, um, I would not know. AdbMonkey (talk) 14:30, 8 November 2010 (UTC)

Glucose test

why does glucose react with benedicts solution? —Preceding unsigned comment added by 173.48.177.117 (talk) 04:53, 8 November 2010 (UTC)

We have an article about Benedict's solution, which explains exactly what sorts of chemicals it reacts with (and the gory chemical details of exactly why those are the ones). We have an article about glucose, with a whole bunch of different types of diagrams...see if you can find one there that has the general functional group type with with Benedict's reacts. DMacks (talk) 04:56, 8 November 2010 (UTC)

As a further hint, compare the oxidation states of an aldehyde versus a carboxylic acid, and copper(I) oxide versus copper(II) oxide. You might want to check reducing sugar. John Riemann Soong (talk) 09:13, 8 November 2010 (UTC)

Can an airship use siphons rather than fans?

I had my own airship question, which I'll file separately to make sure I don't take away from the previous question today.

Is it possible to get good efficiency from an airship by not using fans external to the airship, but simply having siphons that take in air from the front and push it out through a nozzle at the rear? A single chamber that uses some fibers to pull open a cavity at the center of the ship, then allows it to contract should be enough in concept, with one-way baffles at front and rear. Of course, multiple chambers separated by flexing partitions would allow the ship to more continuously take in and discharge air, without needing to change its overall shape. The exact form of the nozzle at rear strikes me as rocket science, about which I'm best off saying as little as possible...

I understand that energy may be wasted if the air is significantly compressed or expanded in the process, since this involves changes in temperature; but in general it seems like such a system should convert the entire energy expended into propulsion. Of course, the real appeal is that one dreams of riding a zeppelin that moves effortlessly and silently among the clouds. Wnt (talk) 12:14, 8 November 2010 (UTC)

You seem to visualise an airborne Jellyfish. Cuddlyable3 (talk) 14:06, 8 November 2010 (UTC)

Sounds to me even more like a low-intensity jet engine. I don't see why it wouldn't be feasible. TomorrowTime (talk) 17:11, 8 November 2010 (UTC)

I doubt it would be efficient. Turbulence in airflow is a lossy process. You can help overcome turbulence by keeping the airflow laminar - that means you need smooth surfaces and continuous air streams. The apparatus described above sounds like it would be "pulsating" - this would incur a huge amount of loss. Every time airflow impinged on a baffle or a valve, it would lose energy; the engine or mechanism used to drive the system would have to compensate by adding more energy. We have a great diagram of thermodynamic efficiencies for various engine concepts - you'll have a very hard time beating a turbofan in terms of specific impulse. They are among the most efficient devices ever built by humans for extracting kinetic energy out of chemical combustion. Nimur (talk) 18:33, 8 November 2010 (UTC)

Brown sugar

I wondered what made brown sugar different than regular sugar, so I looked it up. Now I'm a bit confused. It seems, from what I read, that to make sugar you cut down the cane, process it somehow, and this gives you sugar crystals and molasses. Then, to make brown sugar, you add the molasses back into the sugar. So why bother separating them in the first place? The brown sugar article mentions being able to better control the proportion of molasses to sugar, but is this the only reason? It seems overly complicated just to maintain consistency. Dismas|^(talk) 12:52, 8 November 2010 (UTC)

Well other then quality control, which tends to be rather important nowadays our article also mentions enabling the use of beet sugar while keeping the taste of sugar cane brown sugar that consumers in many countries expect. It's likely cheaper anyway. White sugar refineries produce large quantities of refined white sugar cheaply for the variety of markets which use sugar, diverting some of that production to make brown sugar by adding back some molasses before crystallisation is easier the setting up a seperate production line. Highly refining the sugar also makes it easier to remove unwanted purities other then molasses. This also concurs with the cost in most countries AFAIK (at least in NZ), white sugar is the cheapest, brown sugar is more but less refined sugars are even more. (Well in NZ we also get "raw sugar" which tends to be the same price as brown sugar but I'm not sure what it really is, it tends to be less brown and also far less sticky then brown sugar so I would guess it has less molasses, it's also more granulated.) See [36] for an example of how white sugar is produced. The recent LoGiCane [37] sold in Australia [38] and NZ [39] would be another example where something is added back that was removed although it isn't uncommon in other areas either. Nil Einne (talk) 13:25, 8 November 2010 (UTC)

Counter toxicity

There has been a lot in science journals and what not about the drug salinomycin to kill of cancer stem cells, more than 100 times anything else available at this present time, it also is said that it only kills cancer cells but doesn't disturb other cells. The drug is currently used-produced cheaply, for livestock to kill off their parasites. The tests were done on mice and the major drawback of this drug is that it seems to be very toxic to humans, including possible long term heart problems to muscle problems to being possibly fatal. My question is would it be possible to ever come up with drugs or something else that counteracts the toxicity and could in the future make it possible for humans to use the salinomycin drug to fight cancer? Is it possible to have a counteractive drug against drugs that are toxic or is that a dead end, or in other words once something that is toxic is taken in there is no drugs that can be taken as well to alleviate the toxic effects? —Preceding unsigned comment added by 71.137.248.238 (talk) 14:48, 8 November 2010 (UTC)

There are many drugs that are given together with other drugs that prevent or counteract side-effects of the first one. Whether it's feasible for a specific case depends on how related (at a biochemical level) the desired effects are to the undesired ones. For example, if the drug hits two chemical receptors, a specific agent could possibly be found that prevented the drug from affecting one (preventing the undesired effect when the drug would hit it) while still allowing it to affect the other (leading to desired effect). Or else one could alter the drug itself to be more specific to the target that has the desired effect. On the other hand, if the side-effect and desired effect are both part of the same biochemical pathway, it becomes hard to stop one effect specifically without also stopping the other. Medicinal chemistry and chemical biology are two fields that study how exactly a chemical exerts its effects--what biochemical binding happens, and how the structure of the drug does or does not affect it--and therefore can study how to alter a drug to be more specific or design a related compound that protects against or rescues the "other" biochemical effects. DMacks (talk) 17:48, 8 November 2010 (UTC)

Every drug has a therapeutic window, some narrower than others, and salinomycin apparently has some troubles there. Often it is possible to improve a drug to widen the window, because (as in this case) toxicity may be in one tissue (the heart) while the benefit is in another (the breast tumor). Or they could affect different proteins in the same cell. Through trial and error (most often) or perhaps by identifying the desired and undesired targets and trying to do rational drug design, it is possible to modify the drug so that it won't sit as well in the wrong place, or is more perfectly fits (see lock-and-key model (enzyme)). Alternatively a change in the drug might affect whether cancer cells can get rid of it with P-glycoprotein, or whether it penetrates the blood-brain barrier, or how rapidly it is broken down in the liver (since sometimes the breakdown process causes the toxicity), and any number of such idiosyncratic considerations.

But mostly, people try a lot of different related compounds based on what they can synthesize and hope they get lucky. See high-throughput screening. Also drug discovery and combinatorial chemistry may be interesting. Oh, and last but not least, consider personalized medicine using pharmacogenetics to screen out the patients the drug is most likely to harm. Wnt (talk) 22:23, 8 November 2010 (UTC)

Question

If I has a bag of sand with some marbles in it and I shake the bag of sand, do the marbles end up at the top or the bottom of the bag? —Preceding unsigned comment added by Mirroringelements (talk • contribs) 14:59, 8 November 2010 (UTC)

See Brazil nut effect. TenOfAllTrades(talk) 15:36, 8 November 2010 (UTC)

Gigantism and evolution

So I was reading about Robert Wadlow, and I was wondering if his condition could be passed on to his offspring. Is it possible that some giant animals today exist because an ancestor had a disease that caused excessive growth, and those traits were selected for? ScienceApe (talk) 15:17, 8 November 2010 (UTC)

If by "disease", you mean "genetic abnormality", then yes. But you might want to read about formal definition of disease, as compared to genetic mutation; usually the term "disease" refers to an acquired condition. Most biologists consider the inheritance of acquired traits to be a defunct theory - that means that if the disease that caused a particular trait (like gigantism) was caused by a virus or infection, it is not something that the offspring will inherit. There are a few possible exceptions to this: epigenetics is the modern study of heritable traits by mechanisms other than chromosomal DNA; but I am not aware of any known conditions related to human growth that have such an explanation. A quick search on Google Scholar for epigenetic gigantism turned up Beckwith–Wiedemann syndrome - and that article has a section on genetics that may indicate a developmental condition; but there is stronger evidence for a "random" genetic mutation. Nimur (talk) 18:26, 8 November 2010 (UTC)

Gravitational constant G change

If the gravitational constant were $7.0\times 10^{-11}\ {\rm {N}}\,{\rm {(m/kg)^{2}}}$ (or pick an arbitrarily different value) instead of $6.67\times 10^{-11}\ {\rm {N}}\,{\rm {(m/kg)^{2}}}$, how would the universe be affected? NW (Talk) 17:59, 8 November 2010 (UTC)

You have to precisely specify what this means, as explained by Michael Duff here (see Appendix C for specifically the issue of change in G). One way of making this question meaningful is to multiply G by the square of a mass as is suggested here. Count Iblis (talk) 18:52, 8 November 2010 (UTC)

Is it really possible?

Did (s)he really pull the eyes out like that? Or it's photoshopped? Thanks. —Preceding unsigned comment added by 85.222.86.190 (talk) 18:12, 8 November 2010 (UTC)

Ask yourself what that 'action' would do to the optic nerve and the muscles around the eyeball. You may like to check the anatomy of the human eye. Then think about the pain that would be generated by the 'action' in the photograph. I think you know the answer. Richard Avery (talk) 19:20, 8 November 2010 (UTC)

Kim Goodman can extend her eyeballs by 12mm, which is the world record.[40] That's only about a tenth of the distance implied by the photoshopped image. It's not real. Red Act (talk) 19:52, 8 November 2010 (UTC)

Marty Feldman's face was notable for his bulging eyes, a condition caused by Graves' disease. There are lots of images of him here.Cuddlyable3 (talk) 20:41, 8 November 2010 (UTC)

Sour things

Why is it, that when you eat something sour, your eyes involuntarily squint? Lexicografía (talk) 18:54, 8 November 2010 (UTC)

Something to do with it being astringent perhaps. 92.24.186.80 (talk) 20:44, 8 November 2010 (UTC)

Because pretty much all of the holes in your head are connected. Your eyes are connected to your nose via the Nasolacrimal duct. Your nose is connected to your mouth via the pharynx. So, when you eat something which would burn your eyes if you put it directly into them, it still burns a little because there are ways it can get there. --Jayron32 05:18, 9 November 2010 (UTC)

Lighting circuits

A couple of times, I've turned off the relevant lighting circuit before starting work chaining the light fitting, only to discover that the house's main trip goes at some point during such work. I was under the impression that turning off the lighting circuit would isolate it from doing exactly that. Is something going wrong here? 92.18.72.181 (talk) 19:46, 8 November 2010 (UTC)

Definitely time to call in a licensed electrician to figure out what's going on. If breakers/fuses are set up properly (assuming normal codes), disconnecting there will remove power from the downstream circuits and (as you say) isolate them--there would be no power, and nothing you do would affect breakers upstream of the one you pulled. I've seen all sorts of scary miswirings that can give your results: breaker on the neutral with the hot unswitched, more than one circuit wired into the same switch/junction box (i.e., you only pulled one of the feeds to it), etc. Same (or even more) goes for just turning off a wall switch...there could still be a hot wire into the fixture (before heading out to the switch) or the switch could be on the neutral wire, and jiggling the hot might short it against the junction box or some other connection. Once you're in the nonstandard situation you have symptoms of, I don't think wikipedia can recommend a solution due to potential risks. DMacks (talk) 20:01, 8 November 2010 (UTC)

The OP seems to be in the UK where the mains voltage is 240V AC and not to be messed with. Do not rely on turning off one lighting circuit before working on a light fitting. Most domestic light switches break only one wire and leave the other wire live. Turn off the house's main switch, and if you are sensible like me you will additionally remove the main fuses and check every bare wire with a neon Test light that you know works. Cuddlyable3 (talk) 20:34, 8 November 2010 (UTC)

Didn't even notice the likely UK of the poster. In that case you also get the "fun" of a possible ring circuit, in which you maybe even can't "just turn off" one circuit (again depends on local switching topology). DMacks (talk) 21:07, 8 November 2010 (UTC)

A correctly-wired ring circuit has both ends connected to a single (usually 30 amp) fuse or breaker, and no lighting should be connected to it. I agree that there appears to be some illegal wiring in the house, and strongly recommend that the OP take the advice given above. Dbfirs 21:43, 8 November 2010 (UTC)

I've done this one (I'm in UK). You cut off the lighting circuit (i.e. "live" wire) on the MCB, then you work on the circuit only to find that suddenly all the power goes off. It's because the neutral floats (I've seen 0.8V), and when you touch the neutral to earth, the RCD trips (because the power going down the neutral wire is not the same as the power going down the live wire). It's a pain, all you can do is disconnect the neutral at the box as well.  Ronhjones  ^(Talk) 22:01, 8 November 2010 (UTC)

First if the OP is uncertain she/he should ask a electrician but I think this could be normal as you indicates. I am from Sweden so this may not apply to the OP. If it is the Residual-current device that the OP calls "the house's main trip" it could be due to a low voltage difference between the neutral wire and the protective earth. I do not think it is correct to say that the "neutral floats" since it is still connected to the system. What happens is that there are current flowing through either the protective earth or the neutral on the path to the connection between the protective earth and the neutral (PEN) see Earthing system. This introduce a small voltage difference between PE and N due to voltage drop and if you connect them e.g. by cutting a cable it will result in enough current to trip the Residual-current device. The voltage between PE and N can be due to Neutral return currents through the ground or due to voltage drops along the neutral due to currents from other parts of the installation.Gr8xoz (talk) 22:47, 8 November 2010 (UTC)

Dna Code

Hello, Dna is made up of the four nucleotides (G.A.T.C), thats twice as good as binary. What sort of proteins could be made using only two or more of the existing ones? Is this even possible? Or am I totally understanding things wrong? Is there any fossil records of a simpler form of dna to show how dna evolved to a base of four? Slippycurb (talk) 20:44, 8 November 2010 (UTC) —Preceding unsigned comment added by Slippycurb (talk • contribs) 20:31, 8 November 2010 (UTC)

If there are only two nucleotides, then our existing codon triplet would only allow for 8 different encoded amino acids or else a codon would have to be 4 or more (rather than 3) to give more encoding possibilities (for example, codon quintet would be needed to encode our existing 20ish amino acid choices). Fewer choices would limit the structural variations possible (fewer combinations of polarity, pKa, hydrophobicity, steric bulk, etc.) and also possibly the redundancy/tolerance for mis-pairing during reading or replication. Our Genetic code article is probably a good place to read about these ideas, and also some possible evolutionary history (especially the "Theories on the origin of the genetic code" section, and maybe also the Nucleic acid analogues article). DMacks (talk) 21:02, 8 November 2010 (UTC)

(ec) Proteins are made of chains of amino acids. Base-pairs (a nucleotide and its complementary partner) are grouped in threes, which are called codons. Each codon encodes an amino acid. The transcription process starts at a start codon, then creates by attaching to the protein being created the amino acid corresponding to the current codon, until the stop codon is reached. Our Genetic_code#RNA_codon_table has a list of codon to amino acid mapping, and our introduction to genetics has a lay-man's summary of the process. Coming back to your question, it is believed that originally only the first base-pair of each codon was used; the rest were padding. Then the second was used, and finally the third. The first base-pair makes the biggest change in the coded amino acid, normally from hydrophobic to hydrophilic, (water-attracting to water repelling). The second and third make finer changes, and normally encode for an amino acid that will cause only a slightly worse version of the protein. CS Miller (talk) 21:08, 8 November 2010 (UTC)

If you don't use G and U, you can't start a protein, and GUG start codons are rare anyway; properly you need A, U, and G. And if you don't use U and A you can't stop a protein normally, because all the stop codons contain them. (You could just stop it at the end of the RNA, but then you get non-stop decay...)

On the other hand, sequences using two nucleotides more than others are important. There are wide variations in GC-content between different organisms, sometimes over surprisingly short intervals of evolution. As purines A is like G, and as pyrimidines T and U are like C, and DNA methylation and deamination make transitions between these more common than any other mutation. As a result, you can run across proteins that are composed 70% or more of just two nucleotides. In extreme cases I think you can see evolutionary divergence of the protein as it has tried to reconcile itself to a constant stream of mutations pushing it toward a certain composition, but that's not established that I know of.

I think that most people would agree that the RNA world hypothesis involves the establishment of four nucleotide bases well in advance of the invention of proteins (to permit the level of catalytic activity needed for such aspirations), though there's no hard evidence. Wnt (talk) 21:57, 8 November 2010 (UTC)

baseline characteristics and confounder adjustment in a paper

Hi all I am going to do a presentation reviewing a clinical trial in a few days time. In this trial, the two groups of subjects (control and exposure) differ from each other at baseline in terms of age and smoking status etc. But, at the end of the paper, the authors say that they found an association between their outcome measure and exposure independent of confounders, so my question is do I need to talk about the different baseline characteristics if the authors adjusted for such confounders? Hope I have explained my questions clearly. Thanks, RichYPE (talk) 22:16, 8 November 2010 (UTC)

Wrong answer?

Read question 10 a) ii) : http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/006624/RND01/PH866_paper03.pdf The solution is given here (you have to scroll down below the examiner's comments): http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/006665/RND01/PH866_report_03.pdf Is the solution correct? It seems wrong to me (the Right hand rule tells me otherwise)?. --115.178.29.142 (talk) 22:50, 8 November 2010 (UTC)

Looks okay to me. With your thumb in the direction of the current, your fingers point up on the left (inside the coil) and down on the right (outside) for magnetic field A. This diagram agrees. B obviously goes the opposite way. Clarityfiend (talk) 03:53, 9 November 2010 (UTC)

But the solution has it going down on the left (inside the coil) and up on the right (outside) for magnetic field A. 220.253.253.75 (talk) 04:58, 9 November 2010 (UTC)

Oh, heck. I need to get my eyes checked. It's wrong. Who comes up with these "solutions"? Sarah Palin? Anyway, you're supposed to look at it upside down because you're in Tasmania. Yeah, that's it. Clarityfiend (talk) 05:46, 9 November 2010 (UTC)

Ultimate fate of photon

What ultimately happens to photons after arbitrarily long journey of many billions light years? Can they travel unchanged indefinitely or they do decay, scatter or something? Thanx. —Preceding unsigned comment added by 85.222.86.190 (talk) 23:33, 8 November 2010 (UTC)

They get redshifted due to the metric expansion of space. Red Act (talk) 23:47, 8 November 2010 (UTC)

Beyond that, no time passes from their point of reference, so nothing can happen to them. — DanielLC 01:16, 9 November 2010 (UTC)

Yeah, whether even the redshifting is a "real" change in the photon itself is just a matter of perspective. If my understanding is correct, during a cosmological redshift, the photon's wavelength as measured by cosmological proper distance increases, but the wavelength as measured by comoving distance stays the same. Red Act (talk) 02:47, 9 November 2010 (UTC)

The lifespan of the photon is zero. Neutrino oscillations proved that neutrinos do have a "lifespan" and so the photon sits alone as the only known particle with zero lifespan. Hcobb (talk) 03:06, 9 November 2010 (UTC)

What does "zero lifespan" mean exactly...? WikiDao ☯ (talk) 03:10, 9 November 2010 (UTC)

In the photon's own frame of reference it is created and destroyed in the same instant. Hcobb (talk) 03:13, 9 November 2010 (UTC)

So, in the frame of reference of photons created at about 10 seconds after the Big Bang, the Age of the Universe is... 10 seconds? WikiDao ☯ (talk) 04:15, 9 November 2010 (UTC)

Sort of. Remember that one of the postulates of special relativity is that light cannot be used as a frame of reference, if it is, then there are all sorts of unresolvable paradoxes introduced. One of them is that the photon does not exist in its own frame of reference, that is it has a zero lifespan, i.e. it exists in OUR frame of reference, but in its own it wouldn't exist for any measurable time. Another perspective on the same paradox is that, from light's frame of reference, the entire universe happens simultaneously, that is all events occur in the same instant. Don't try to rap your mind around this things, unlike some of the unintuitive paradoxes such as the twin paradox, which actually occur, these are real physical impossibilities, do we generally don't even ponder what life is like in lights frame of reference. For all intents and purposes, it doesn't exist. --Jayron32 05:12, 9 November 2010 (UTC)

Now imagine a substance so strange that it slows a beam a light down by a large enough fraction that you'll notice the difference. What does that say about the lifespan of a photon? I'd suggest sitting down with a glass of water while you think about it. Hcobb (talk) 06:48, 9 November 2010 (UTC)

The fact that the local speed of light in a medium is slower than it is in a vacuum doesn't change the nature of the speed of light. The speed of light in water is still invarient, and still presents the same limits in water as does the speed of light in a vacuum. Slow light covers some of this. That the photons slow down in water doesn't change the fundemental nature of the photons. --Jayron32 06:59, 9 November 2010 (UTC)

November 9

what animals can humans coproduce with?

since a donkey plus a horse can breed a mule, what animals can a human coproduce with, and what are the resulting animals called?

also, have most combinations been tried or is it possible a lot of viable (though, like the mule, possibly sterile) combinations simply were never tried yet? Thanks. 85.181.151.31 (talk) 00:08, 9 November 2010 (UTC)

Neanderthals. Count Iblis (talk) 00:14, 9 November 2010 (UTC)

Certainly as much an "animal" as homo sapiens sapiens, but still a human animal:

"Neanderthals are either classified as a subspecies (or race) of modern humans (Homo sapiens neanderthalensis) or as a separate human species (Homo neanderthalensis)."

according to the Neanderthal article.

There is, of course, no separate species today with which humans could co-produce, OP. I hope that resolves your interest in this question, but in case not I will put up the "{{RD-alert}}" tag. :| WikiDao ☯ (talk) 00:33, 9 November 2010 (UTC)

We do also have articles on the hypothetical humanzee and on parahuman. That's all I found in Category:Mammal hybrids, apart from the already mentioned Neanderthal admixture hypothesis. ---Sluzzelin talk 00:38, 9 November 2010 (UTC)

That's two corrections on assumptions-about-answerability-of-questions in a row, Sluzzelin – I promise I'll get with it by the third! :) WikiDao ☯ (talk) 00:45, 9 November 2010 (UTC)

It remains controversial whether or not Neanderthals could breed with anatomically modern humans (or more precisely whether genes were exchanged between the populations, which would require non-sterile offspring). Until a few years ago, most genetic studies suggested no genes were transferred from Neanderthals to humans, but in recent years the arguments have tended to support a limited amount of gene transfer. Dragons flight (talk) 01:16, 9 November 2010 (UTC)

Any information given in response to this question should be prefaced Do not try this at home . An aid to remember this warning is this extract from the article Origin of AIDS: ...the virus originated in populations of wild chimpanzees in West-Central Africa...scientists calculate that the jump from chimpanzee to human probably happened during the late 19th or early 20th century, a time of rapid urbanisation and colonisation in equatorial Africa. Cuddlyable3 (talk) 11:03, 9 November 2010 (UTC)

I, the OP, (different IP now) was not thinking of sexual intercourse with 'em, but rather artificial insemination. Have they tried inseminating all the animals in zoos with human sperm to see if any give birth to viable young? Obviously I'm thinking of primates rather than dolphins and such. 84.153.236.235 (talk) 11:14, 9 November 2010 (UTC)

I'm not really much of a scientist/biologist, but aren't there a whole raft of laws to prevent people doing that sort of thing - It strikes me as something that would be seen as highly un-ethical, and likely quite illegal. Forgive my naivety if this is not the case Darigan (talk) 11:33, 9 November 2010 (UTC)

Did you read the linked article, humanzee? That also links to Ilya Ivanovich Ivanov (biologist) which may provide more details Nil Einne (talk) 13:34, 9 November 2010 (UTC)

Why doesn't cryonics just use a ton of insulation?

From my understanding, cryonics requires replacing the liquid nitrogen every week or so. Insulation decreases thermal conductivity exponentially with distance, so why not just use so much insulation that the temperature stays low until the singularity? — DanielLC 01:47, 9 November 2010 (UTC)

Thermal conductivity is linear in thickness not exponential. Dragons flight (talk) 02:37, 9 November 2010 (UTC)

And liquid nitrogen is cheap when compared to real estate! Physchim62 (talk) 03:56, 9 November 2010 (UTC)

As you increase the amount of insulation, you also increase the surface area over which you're gaining heat. For this reason, there is an optimal insulation thickness. (I don't have the book with me, but see Transport Phenomena by Bird, Stuart, and Lightfoot, I believe there's an example problem like this.) shoy (reactions) 13:03, 9 November 2010 (UTC)

desk chair

the arm of my chair tore open and the stuffing is exposed. the stuffing looks like a black tee shirt put thru a meat grinder. what kinda stuffing is this? —Preceding unsigned comment added by Kj650 (talk • contribs) 02:03, 9 November 2010 (UTC)

It may be exactly what it looks like. It's very common to recycle old textiles as stuffing. Ariel. (talk) 04:44, 9 November 2010 (UTC)

wouldent cotton get moldy? —Preceding unsigned comment added by Kj650 (talk • contribs) 05:38, 9 November 2010 (UTC)

If it got wet, it could. If old shirts are used, they are likely treated with some sort of anti-bacterial/anti-microbial solution to keep them from getting mold simply from perspiration and skin oils. Dismas|^(talk) 05:40, 9 November 2010 (UTC)

You need moisture for mold to grow, so as long as it stays dry it won't mold. A single spill is not enough either, it would need to stay wet for about 2-3 days. Ariel. (talk) 06:22, 9 November 2010 (UTC)

street lighting

metal halide lamps vs sodium vapour. —Preceding unsigned comment added by 59.161.130.15 (talk) 03:58, 9 November 2010 (UTC)

What about it and them? We have a Street light article that mentions and compares various technologies. DMacks (talk) 04:40, 9 November 2010 (UTC)

Inclined plane, Non-conservative forces help

A block of weight 8N is launched up a 30 degree inclined plane, of length 2 m by a spring, with spring constant 2 kN/m and a maximum compression .1 m. The average force on the block due to friction & air resistance, combined, has magnitude 2 N. Does the block reach the top of the incline? If so, how much kinetic energy does it have at the top; if not, how close to the top does it get?

Okay--so here's my approach, PE(initial)=PE(final) + KE (final) + Work(nonconservative)

the initial PE is (1/2)kx^2=10J, PE final=mgh=(8N)(2sin(30))=8J Work done by NC forces=(2N)(2m)=4J

Ergo: 10J=8J+[(1/2)mv^2]-4J 6J=KEfinal by those maths, it seems to me that it does reach the top, with 6J of KE at the top. Is my reasoning sound?24.63.107.0 (talk) 04:06, 9 November 2010 (UTC)

Oldowan tools experiment

(I originally posted this at the Humanities desk, but maybe it ought to be here.) The author of this book review states, in passing, "Experiments have shown that Oldowan tools can be made using just the part of the brain that was available back in Homo habilis times." Is that true? What was the nature of these experiments? I can't find anything at the Oldowan article. LANTZY^TALK 06:31, 9 November 2010 (UTC)

hydrogenated ketone

whats a hydrogenated ketone —Preceding unsigned comment added by Kj650 (talk • contribs) 08:28, 9 November 2010 (UTC)

Could have many meanings depending on context. Could be an alcohol (the result of hydrogenating a ketone), could be a ketone in an alkane structure (the result of hydrogenation of an alkene). DMacks (talk) 08:59, 9 November 2010 (UTC)

Stereogram effect

While watching TV recently I saw an interesting effect whereby a photograph seemed to be stereoscopic, the camera moved away and to one side and the images in the photograph appeared to be separate and give a stereo effect. I can understand how a two eyed viewer achieves a stereo effect but this was with a (?)single lens camera. I have also seen the same thing with what appear to be paintings. What is this effect called and how is it achieved? Caesar's Daddy (talk) 09:06, 9 November 2010 (UTC)

For real scenes the effect is achieved by taking pictures simultaneously by a horizontal row of cameras. As the viewpoint moves sideways the display morphs from camera to camera giving the illusion of parallax that continually varies with viewing position. You may notice that the range of movement is seldom wide, because cameras are expensive.Cuddlyable3 (talk) 10:44, 9 November 2010 (UTC)

(EC) This is described somewhat in Stereoscopy#Wiggle stereoscopy, Stereopsis and Parallax Nil Einne (talk) 10:47, 9 November 2010 (UTC)

How do you compare grades?

If a candidate has an A in the course 101 and the second candidate has an A in the course 101 and a C in the course 202, the second would have lower grades, but more knowledge, wouldn't he? So, drawing the average doesn't seem always appropriate. How is this done in real life? How do you call this kind of mistake? (drawing the average when you shouldn't do it). Quest09 (talk) 13:13, 9 November 2010 (UTC)

GPA is known to be faulty. A common fix is to weight harder courses with an extra point. So, a B in a harder course is worth an A. That is how you end up with something like my high school GPA of 4.2 out of a 4.0 scale. In the end, it doesn't really matter. Nobody ever asks me what my high school GPA was. Nobody cares about my cum laude with my B.S. degree. I don't even have grades for my PhD. The degree is all that anyone cares about. -- kainaw™ 13:28, 9 November 2010 (UTC)

Where is Steve Baker???

Nothing to do with science (or maybe very much to do?)

 TY