Wikipedia:Reference desk/Archives/Science/2010 November 5

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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)