Wikipedia:Reference desk/Archives/Science/2010 October 30

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October 30

Carbonated drinks and digestive health?

This is a bit speculative here and there might not be a definitive answer:

If it's true that neurotransmitters are reduced in reaction to a receptor being stimulated... So, for instance, capsaicin which normally causes pain and inflammation can also be a treatment for reducing pain and inflammation...

And if there is something like pressure receptors somewhere in the GI tract (mechanoreceptors?? osmoreceptors?? some other name??)...

...Then, in the long-term, couldn't carbonated drinks lead to digestive problems (in the short-term, carbonated drinks can lead to borborygmus, right? In the long-term, couldn't they cause GI pressure to be poorly regulated?) ☯  Zenwhat (talk) 01:24, 30 October 2010 (UTC)

My anecdotal experience is that excessive CO₂ can lead one to feel a little gassy, but it is usually vented pretty quickly. I'm not sure I see things hanging around enough, or having significant physiological effect, to have long-term effects of the sort you're describing, but I'm no anatomist. --Mr.98 (talk) 02:59, 30 October 2010 (UTC)

Since the gastrointestinal cavity is not rigid, any accumulation of gas causes bloating, which is not at all difficult to detect, unfortunately. Looie496 (talk) 03:49, 30 October 2010 (UTC)

uakari fruits

What is the name of the fruit that Bald Uakaris eat in order to produce more babies? —Preceding unsigned comment added by 70.31.22.155 (talk) 01:38, 30 October 2010 (UTC)

Our Bald Uakari article says: "The overall diet of a uakari consists of 67% seeds, 18% fruit, 6% flowers, 5% animal prey, and buds. They will also eat insects that happen to be cross their path, however they do not specifically pursue this type of food." It also says: "Their powerful lower jaw forms a pseudodental comb, which allows the uakari to open the hard surfaces of unripe fruits and eat the nuts that most other primates would not be able to open," but it doesn't say specifically what they might eat that would affect their reproductive behavior. WikiDao ☯ (talk) 01:59, 30 October 2010 (UTC)

Time dilation? Time speeding?

Dear friend, I have difficulty understand the beginning of the section {Time dilation and length contraction} in Special Relativity, Could some one tell me what should I say to respond the LAST suggestion from DVdm in the following conversation? Please help.

Regards, John

Discussion at Talk:Special_relativity#Time_dilation_and_length_contraction.

== Time dilation and length contraction == THE BEGINNING OF THIS SECTION IS NOT CLEAR. PLEASE REVIEW WITH THE CAPITAL CHARACTERS. See also: Twin paradox Writing the Lorentz transformation and its inverse in terms of coordinate differences we get △t’=γ(△t-(v△x/c^2)) DOES {in terms of coordinate differences} MEANS (T2’-T1’)=γ((T2-T1)-(V(X2-X1)/C^2))? △x’=γ(△x-v△t) and △t=γ(△t’+(v△x’/c^2)), △x=γ(△x’+v△t’) Suppose we have a clock at rest in the unprimed system S. Two consecutive ticks of this clock are then characterized by Δx = 0. If we want to know the relation between the times between these ticks as measured in both systems, we can use the first equation and find: △t’=γ△t (for events satisfying Δx = 0) DOES {the relation between the times between these ticks} MEANS ABOVE EQUATION, △t’=γ△t, IS FOR TICKS T2’=M+1 AND T1’=M FOR △t’, THEN, T2=N+1 AND T1=N FOR △t? IF THAT IS WHAT IT MEANS, THEN △t’=γ△t MEANS 1=γ*1, SO THAT γ=1 AND △t’=△t, NO TIME DILATION. IF THAT IS NOT WHAT IT MEANS, THEN COULD SOMEONE TELL ME WHAT DOES IT MEAN? This shows that the time Δt' between the two ticks as seen in the 'moving' frame S' is larger than the time Δt between these ticks as measured in the rest frame of the clock. This phenomenon is called time dilation. COULD SOMEONE REWRITE IT? Regards, John Huang Jh17710 (talk) 05:37, 24 October 2010 (UTC) The way that section Special relativity#Time dilation and length contraction is written, the observer would have to be in the primed reference system and the clocks or measuring rods being distorted would have to be in the unprimed reference system. This is the reverse of way that I would have chosen to do it, if it were up to me. But either way should work if the text explained it well, which it does not. JRSpriggs (talk) 15:21, 24 October 2010 (UTC) I think the text explains it very well. Starting from the standard transformations, it indeed takes the "moving" clock/rod in the unprimed sysem (thus with "proper" time/length in unprimed coordinates) and calculates the coordinates in some other system, using some set of "primed" coordinates. DVdm (talk) 18:02, 24 October 2010 (UTC) Thanks for your note, JRSpriggs. It is really hard to stay posted in Wikipedia, but, I will try to follow their regulations.Jh17710 (talk) 15:43, 24 October 2010 (UTC) John, you cannot combine the equations for time dilation and length contration the way you tried to do it. When you do that, you effectively combine two events satisfying both Δt’=0 and Δx = 0. When you look at the transformation equations, you will notice that this can be only be valid for two events satisfying Δt’ = Δt = Δx' = Δx = 0, in other words for equations of the form 0=0. You deduced "... THEN Δt’=γΔt MEANS 1=γ*1, SO THAT γ=1 AND Δt’=Δt, NO TIME DILATION", but you forgot the case Δt’=Δt=0, from which 1=γ*1 does not follow. You "divided by zero", so to speak. I think this was explained to you a few times before somewhere on Usenet. DVdm (talk) 18:02, 24 October 2010 (UTC) Thanks a lot, DVdm. You are the person I need to talk to. I thought that some thing wrong in this short paragraph, from "Writing..." to "...is called time dilation." because I was unable to explain the "△t’" mathematically to fit in the "Two consecutive ticks of this clock". I asked for help. Your answer to JRSpriggs did not mention about any detail of the CALCULATES THE COORDINATES like using regular concepts of {a time period △t’}, which is normally represented by {from time t1' to another time t2', so that △t’=(t2'-t1')}. What is the mathematical value of the first tick of that clock and what is the value for the next tick of that clock? If there is no such value, then, don't use "△t’", use something else like Ut' to represent the time period between two consecutive ticks of the moving clock. However, if you do so, you must figure out how you adjust the equations of LT to fit your Ut' and Ut. We know that △x’=γ(△x-vUt) and Ut’=γ(Ut-(v△x/c^2)) is not going to fit for every event location with x-coordinate x in the stationary system and x'-coordinate x' in the moving system. Could you provide more detail regarding your statement "I think the text explains it very well."? Thanks. Regards, JohnJh17710 (talk) 19:54, 24 October 2010 (UTC) John, if you have problems with the special relativity theory, please ask on the wp:reference desk/science. Please read the wp:talk page guidelines: this article talk page is for discussing the article, and not for discussing the subject. It is also not for educating those who have problems understanding the subject. This was explained to you on your old talk page User talk:John C. Huang many times. I have left a new warning on your new talk page User_talk:Jh17710. Good luck (and look) at the reference desk. DVdm (talk) 20:33, 24 October 2010 (UTC) Thanks DVdm. As you can tell, I just try to make this section more reader friendly. My main point is that, the usage of a popular symbol △t in this section is very different from popular definition. As I know, △t is for the difference of two times, △t=(t2-t1), so that I hope someone can bridge the gap. The evidence is in the statement {the time Δt' between the two ticks (of the clock in S) as seen in the 'moving' frame S'}. There is no t2' and t1' so that it looks like Δt' represents the time interval for one unit of time in S'. That means it will be miss recognized as Δt'=1, and the same for Δt=1. I mean, physically, {the one unit of time} in S' is larger than {the one unit of time} in S, that is clearly described but mathematically it is not presented properly. Hope you can improve it. Especially, when you think about the popular time equation of SR, t'=t/γ, which is also true for △t'=△t/γ with regular definition as (t2'-t1')=(t2-t1)/γ; don't you think this section needs some modification? Regards, JohnJh17710 (talk) 00:32, 25 October 2010 (UTC) I don't think it is necesserary to explicitly mathematically present the definitions of the Deltas, since everything is well explained in words, but I did it anyway. Hope this helps. DVdm (talk) 07:07, 25 October 2010 (UTC) Thanks DVdm. Now, we have △t for the difference of two times, △t=(t2-t1). In this paragraph, t1 will be the time of the first tick in S and t2 is for the time of the second tick in S. If we arrange the clock to stay in S, we will derive △t'=γ△t like in the current paragraph; if we let the clock to stay in S', like what Einstein did in his paper dated 6-30-1905, then we will derive △t'=△t/γ, like what Einstein had derived before. That is why JRSpriggs said {This is the reverse of way that I would have chosen to do it, if it were up to me.} The reason original paragraph did make sense physically is, if △t' means the length of {one unit of time} in S' and △t means the length of {one unit of time} in S, then △t'=γ△t did clearly mean time dilation. To avoid 1=γ*1, it can be written like 1s'=γ*1s, or Ut'=γUt. However, if we use 1s' to represent the length of <time unit> in S', and 1s to represent that in S, then the definition of 1s' and 1s will make them not compatible with Lorentz equation. Then, we need to figure out some other way to use the symbols 1s' and 1s to explain time dilation. I think, probably, if we let that reference clock stay in S' for now, we will have more time to find a proper solution for 1s' and 1s, or Ut' and Ut. It will be nice if we can see one unit of time in S' is longer than one unit of time in S mathematically, because it makes more sense, physically. Regards, JohnJh17710 (talk) 04:09, 26 October 2010 (UTC) You've got it all wrong and you clearly do not understand the setup. The text clearly explains that the clock is at rest in S, so, when we have two consecutive tick events on that clock, then Δt can indeed mean the " length of one unit of time in S ", but then Δt' does not mean the " length of one unit of time in S' ". Δt' would then mean the " length as measured in S' of one unit of time in S ", and the equation Δt' = γ Δt expresses time dilation. I don't think there is more clear way to explain this than is done in the text. If you really do not understand this, then I strongly suggest that you go elsewhere to have it explained to you. This is not the place for that. DVdm (talk) 08:29, 26 October 2010 (UTC) You are right about the setup, {Δt' would then mean the "length (t2'-t1')Ut' as measured in S' for one unit of time 1*(Ut) in S}. But, in that setup the equation Δt' = γ Δt expresses time speeding, not dilation, because for all |v|<c, we have γ>1 and Δt'>Δt. Assume that γ=5, we will have Δt=1 and Δt'=5, that means {the event of two ticks in S} is measured as 1*Ut in S and measured as 5*Ut' in S'. That means Δt'=5*Ut'=1*Ut=Δt, Ut'=Ut/5; the clock in S' is running faster. But, Einstein wanted it the other way. Isn't it?Jh17710 (talk) 02:21, 27 October 2010 (UTC) I think you might find someone to help you understand some basics on the wp:Reference desk. This is not the place. I have put a 3rd level warning on your talk page (User talk:Jh17710) DVdm (talk) 12:24, 27 October 2010 (UTC)

Thanks. JohnJh17710 (talk) 04:04, 30 October 2010 (UTC)

I see you haven't had any luck so far in getting your question answered. As a suggestion, perhaps you'd have better luck getting an answer if you repost your question as a paragraph that's as brief as possible, while still containing all the information that's essential to understanding what it is that you're asking. A question is a little less daunting to the volunteers if the question can be understood by just reading one brief paragraph, rather than having to read through an entire lengthy conversation to see what's going on. Red Act (talk) 02:29, 31 October 2010 (UTC)

Stained glass

Resolved

Is there any way of finding out when a particular stained glass window was made and by whom and as a result determine if the artist died more than 70 years ago?

During what has turned out to be a successful GA review of St James' Church, Stretham the reviewer drew my attention to a potential Freedom of Panorama issue with the image I took of the church's stained glass window, File:St James Church Stretham window 06-09-2010.jpg, licensed as {{cc-by-3.0}} i.e. my own work. I raised the issue at the media copyright questions forum here. The church plans website ("Stretham, St James' (1874-76)". Church plans online. Lambeth Palace Library. Retrieved 26 August 2010.) indicates that the church was restored between 1874 and 1876 by architect J. P. St Aubyn. Heavily restored, according to VCH (T.D. Atkinson, Ethel M. Hampson, E.T. Long, C.A.F. Meekings, Edward Miller, H.B. Wells, G.M.G. Woodgate (1953), Pugh, R.B. (ed.), The Victoria History of the Counties of England: Cambridge and the isle of Ely, vol. IV, Oxford University Press, pp. 151–159{{citation}}: CS1 maint: multiple names: authors list (link)). Indeed, VCH records "The chancel has an east window of five lights with modern geometrical tracery, and there is a hood-mould terminating in heads". Does this mean modern in the 1953 (VCH) sense or modern in the not medieval sense? Pevsner is no help either.

The VCH was originally published in the first decade of the 20th Century, so IMHO Victorian would probably be "modern". Alansplodge (talk) 14:33, 30 October 2010 (UTC)

Short of going down to the Cambridgeshire Archives (hard but not impossible for me) or the Lambeth Palace Library (nearly impossible for me) I am not sure how I can determine who made this stained glass window and when. In any case, would such trips constitute OR? Just for completeness, I have asked the church's team vicar and one of the church wardens; neither can help

--Senra (Talk) 11:17, 30 October 2010 (UTC)

I've always found Cambridgeshire Archives most helpful by phone, could you try ringing them? --TammyMoet (talk) 11:24, 30 October 2010 (UTC)

The image you took, second pane from right, bottom - "AD MDCCCLXVIII" = 1868? I would guess that dates the glass though it could refer to an event portrayed in the image - however the image appears to be the Ascension of Christ so I think it's the date - there's also a name "Henricus Herveius Baber" on the second pane from the left - is this the artist (or benefactor)? I would guess the date refers to a commisioning date rather than installation - which would fit with a 1870s restoration. (maybe) Sf5xeplus (talk) 11:40, 30 October 2010 (UTC)

Ha ha. I'm an idiot. Every artist signs their work don't they? Well then Shylocke (aka Sf5xeplus), I am going to agree with you on the date, thank you. However, Henry Hervey Baber was a vicar of Stretham serving from 1827–1869. Also reading my way through British and Irish stained glass (1811–1918) at the moment too --Senra (Talk) 11:48, 30 October 2010 (UTC)

Is it concievable that the vicar, Henry Hervey Baber actually designed the window? --Senra (Talk) 11:52, 30 October 2010 (UTC)

(It's conceivable.. You mean't Sherlock? not Shylock? I haven't lent you any money yet ?! )Sf5xeplus (talk) 11:54, 30 October 2010 (UTC)

(Concievable was my bad spelling and Shylocke was a freudian slip as I know someone called Shylocke) --Senra (Talk) 12:03, 30 October 2010 (UTC)

Actually I meant It's conceivable that he designed the window - I didn't even notice the spelling mistake. Sf5xeplus (talk) 12:47, 30 October 2010 (UTC)

According to our article this Henry Hervey Baber popped his clogs in 1869 - maybe it's a memorial? (or paid for by him as part memorial?)Sf5xeplus (talk) 12:05, 30 October 2010 (UTC)

Out of curoisity, how did you get such a straight image (no parallax) - special lens, ladder or photoshop ? Sf5xeplus (talk) 12:12, 30 October 2010 (UTC)

Very careful use of Photoshop CS4's perspective and vertical scale (i.e. corrected the perspective then corrected the resulting foreshortening) though I did not measure it; I relied on the mark one eyeball --Senra (Talk) 12:22, 30 October 2010 (UTC)

Following your above question and assuming no parallax in this image, I have just measured the two images. The window in this view measures 8.9 x 8.25 whilst the window in this view measures 70 x 68 which is 3.3 mm too short - not bad for mark one eyeball! --Senra (Talk) 12:33, 30 October 2010 (UTC)

Just some general background on English church stained glass. Surviving medieval stained glass is quite rare, as much of it was destroyed during the English Civil War in the 17th Century. Stained glass depicting religious scenes didn't really re-appear until the second half of the 19th Century, when the Oxford Movement co-incided with the Arts and Crafts Movement. Before that, it would have been considered "popish" except if it showed secular subjects - family crests were common. They became the most popular sort of memorial for parishoners (by late Victorian times, grand memorial tablets were considered a bit vain). The windows would often carry the name and dates of the deceased - "the dedication" - or it might be on a small plaque underneath, usually "To the Glory of God and in Memory of...". I've never seen a church stained glass with the artist's name on it. The east window of my church has the name of a local builders' merchants on it; apparently you could pick one out of a catalogue. I'm certain this would have been a memorial to Henry Hervey Baber commissioned soon after his death. Alansplodge (talk) 13:02, 30 October 2010 (UTC)

Just a note that although church windows are traditionally not "signed" by the artist, many of them will bear the designer's monogram. You can see one here.--Shantavira|^{feed me} 14:35, 30 October 2010 (UTC)

I stand corrected. There's rather a good index of makers' marks here[1], mostly quite inconspicuous. This one - Comper, J Ninian - has a strawberry plant as their mark[2]. Thanks Shantavira, I'll look more closely in future. Alansplodge (talk) 16:23, 30 October 2010 (UTC)

Facinating. Makers marks; memorials; arts and crafts; and all despite my bad spelling!

I have sent an email to Cambridgeshire Archives. In the meantime, I am not certain this window is a memorial to Henry Hervey Baber as he died in 1869 and the date on the glass is 1868. Additionally the restoration was later (1874–1876). I have also carefully examined every inch of the image without finding any marks although the highlights are a little blown making it hard to see a makers mark if it is there. I guess I need to make another visit to the church whilst hoping Cambridgeshire Archives can help too. Thank you to everyone who has taken the time to reply above.

--Senra (Talk) 18:48, 30 October 2010 (UTC)

Issue resolved by Elen of the Roads (talk · contribs) at Wikipedia:Media copyright questions#Stained glass window .28UK.29 Panoramafreiheit.3F

“ Stained glass windows are considered works of artistic craftsmanship and therefore subject to UK freedom of panorama. Stained glass in a building which is open to the public (which churches have to be in the UK to get exemption from the rates) can be photographed without breach of copyright. ”

--Senra (Talk) 22:30, 30 October 2010 (UTC)

Is it possible to create an exotic atom with antiprotons instead of electrons?

With the antiprotons in a stable orbital shell around the nucleus. Can this be achieved? ScienceApe (talk) 14:36, 30 October 2010 (UTC)

"Massive particles in cloud around nucleus" doesn't sound anything like an "atom" at all (would it be possible to condense a bunch of antielectrons into a dense enough core to form a "nucleus" of your thing)? There sure is antimatter, but it's still got the same particle masses in the same "places". DMacks (talk) 14:52, 30 October 2010 (UTC)

I'm no physicist but it strikes me that if you couldn't do it with regular protons, you couldn't do it with antiprotons. The charge is not what makes them act like protons or electrons in the sense you mean here (which can form nuclei, which form clouds); they have fundamentally different properties and constituent parts separate from their charge. --Mr.98 (talk) 15:13, 30 October 2010 (UTC)

(ec)Have you read Muonium, and Positronium? It doesn't look like antiprotons are easy to create; so there is little experimental work with even short-lived antiproton species. Nimur (talk) 15:21, 30 October 2010 (UTC)

I think the proposition was that you'd have a nucleus full of antielectrons surrounded by a cloud of antiprotons — maintaining the charge locations of a standard atom (positive nucleus, negative cloud), but with antiparticles. I don't think that will work — electrons/antielectrons are just not going to work in a nucleus, and protons/antiprotons are not going to behave like an electron cloud. It's not the same thing as nucleus of antiprotons surrounded by a cloud of antielectrons, which is certainly possible (antihydrogen). But I'm no physicist. --Mr.98 (talk) 16:03, 30 October 2010 (UTC)

Ok what about anti-neutrons instead of neutrons in what would otherwise be a normal atom? Would they annihilate with the normal protons? ScienceApe (talk) 15:19, 30 October 2010 (UTC)

Yes, the anti-quarks will combine with quarks to form pions which will then decay. But, as far as the original question is concerned, you can actually form a short lived "atom" consisting of a proton and an anti-proton. When a proton and an anti-proton meet they will actually form a bound state at some high lying energy level. Then the system makes transitions to lower lying levels, eventually making the transition to the final state where the proton and anti-proton have annihilated. Count Iblis (talk) 15:56, 30 October 2010 (UTC)

I see we have articles on antihydrogen, which has been made; antideuterium hasn't been. Antiprotonic helium is an antiprotonic atom for which an article has been started; I suppose you can mix an antiproton into anything. Wnt (talk) 18:53, 30 October 2010 (UTC)

Isn't what prevents the proton from "annihilating" the electron (to form say, a neutron) is that the electron has much too fast to be absorbed? John Riemann Soong (talk) 23:24, 30 October 2010 (UTC)

No, Protons don't spontaneously abosorb electrons to form neutrons because neutrons are heavier them the sum of the masses of an electron and a proton so that there is an energy gap that would have to be bridged in order for the reaction to occur. 76.123.74.93 (talk) 03:52, 31 October 2010 (UTC)

That process - adding an electron and a proton to "yield" a neutron, is called Electron capture. It can only occur in certain circumstances. It is in some sense the time-reversal of β− decay. Nimur (talk) 21:41, 1 November 2010 (UTC)

The ground state of the electron in an atom is far from the nucleus. The antiproton is much heavier and so it will radiate photons and drop down until contact with the nucleus and boom. Hcobb (talk) 21:55, 1 November 2010 (UTC)

Woodchip bug

Anyone know what species this insect is? It's camouflaged to look like a woodchip=P.Smallman12q (talk) 16:32, 30 October 2010 (UTC)

Try asking whatsthatbug.com. SmartSE (talk) 23:39, 30 October 2010 (UTC)

Go on, give us a clue. Whereabouts on the planet did you see it? Alansplodge (talk) 11:52, 31 October 2010 (UTC)

I saw it amongst some shrub trimmings in New York. Almost crushed the poor critter... My camera phone had a hard time focusing on it. I'll give whatsthatbug.com a try if Wikipedia doesn't come up with an answer (these ref desks are usually quite good=D).Smallman12q (talk) 13:57, 31 October 2010 (UTC)

I'm pretty sure its a moth, but being in the UK I don't know enough about (or have references on) American lepidoptera to try narrowing it down much further. You might also try asking on the appropriate forum at Ask a Biologist. 87.81.230.195 (talk) 02:35, 1 November 2010 (UTC)

volcanic tropical cyclones

If weather conditions are just right when a volcano erupts and causes an ash cloud to blow over tropical waters is it possible for a tropical cyclone to form. --213.94.238.235 (talk) 18:19, 30 October 2010 (UTC)

Probably not. Tropical cyclone formation requires evaporation from the sea surface, and the ash would block sunlight from reaching the water. In the Atlantic, there are sometimes surges of dust that blow from the Sahara, and they suppress cyclone formation while the dust is in the air. Looie496 (talk) 19:42, 30 October 2010 (UTC)

Pure energy

What does pure energy look like? --75.33.217.61 (talk) 18:52, 30 October 2010 (UTC)

Either "nothing", "it does not exist", or "it depends on its wavelength"--take your pick. DMacks (talk) 19:04, 30 October 2010 (UTC)

To answer that question, you'd have to define what you mean by "pure" energy. If by "pure energy" you mean a form of energy that has no properties other than energy, then the answer is that we can't see pure energy. The only thing our eyes are capable of seeing is light. And the photons of which light consists not only have energy as one of their properties, but also have nonzero spin, so they wouldn't count as "pure energy" according to the above definition. On the other hand, if you define "pure energy" as massless forms of energy, then light would count as "pure energy", so everything that your eyes are capable of seeing is pure energy, since ultimately, all you can see is light. Red Act (talk) 19:21, 30 October 2010 (UTC)

By the way, if by "pure energy" you mean a form of energy that has no properties other than energy, then pure energy doesn't even exist. All of the elementary particles that everything in the universe is ultimately made out of have one or more properties other than energy. Red Act (talk) 19:30, 30 October 2010 (UTC)

And as far as what Pure Energy looks like, the cover art looks rather comic book-y, and the band members themselves consider it to look "dreadful"[3] and "like some 10-year-old's school notebook drawings"[4]. Red Act (talk) 19:43, 30 October 2010 (UTC)

Choose any picture here. Cuddlyable3 (talk) 22:39, 30 October 2010 (UTC)

(re RedAct) I'm fairly certain an answer is light .. sure photons have spin - but that is the handle by which the photons 'carry' the energy - eg a photon with 0 energy doesn't exist.87.102.72.130 (talk) 13:05, 31 October 2010 (UTC)

Yes, that's a perfectly reasonable answer. "It doesn't exist" is also a perfectly reasonable answer. "Pure energy" doesn't have any standard scientific meaning, so the question as posed is ill-defined. Unless and until the OP provides a definition for what "pure energy" is to be taken to mean, there is no one "correct" answer. Red Act (talk) 01:17, 1 November 2010 (UTC)

DC Circuits - resistors

O.K., so this is homework, but I'm totally bewildered on a particular point. We've been asked to calculate the current in a branch of a circuit where there is a resistor which has resistance 'approaching zero and infinite ohms'. I'm fine working out the currents / voltages if there are numbers involved - loop rule, junction rule etc, but the infinite bit??? Is it anything to do with moving a charge from infinity, i.e. potential difference? ThanksSophiepuss (talk) 19:35, 30 October 2010 (UTC)

The exact text of the question would help. Is it two cases "(1)resistance approaching zero; (2) resistance approaching infinity," or is it a single impossible circuit element whose resistance approaches both zero and infinity at the same time? It sounds like if it is two cases, a single pole single throw switch would be the circuit element to consider, since it could be close to zero or close to infinite resistance. Edison (talk) 20:02, 30 October 2010 (UTC)

(EC) If a resistor has infinite ohms, it's basically the same as if the resistor was completely removed from the circuit. There is zero current flowing through a resistor with infinite ohms. Red Act (talk) 20:07, 30 October 2010 (UTC)

A zero resistance element will have zero voltage dropped across it, and other resistances as well as the voltages in the circuit will determine the current through it. Edison (talk) 00:53, 31 October 2010 (UTC)

A teaching/learning note for the OP. Part of the reason for asking this type of question is to take you beyond the "I'm fine working out the currents / voltages if there are numbers involved..." stage. Your formulae may not work with zero/infinity, but they will work with numbers approaching those figures. So do your calculations using 0.1, 0.01, 0.001... and see what happens; this will point you towards what happens as you approach zero, and from that you should be able to extrapolate to what will most likely happen at zero. Then do the same using very large numbers for the case of approaching infinity. (And a slight warning - with some physical situations zero and/or infinity may be special cases with quite unexpected results, but if that's the case questions usually won't be framed in this way unless you've been taught the special cases). --jjron (talk) 04:06, 31 October 2010 (UTC)

If the resistance approaches 0, replace the resistor with wire and think about what happens. If it approaches infinity, remove the resistor and see what happens. --99.237.232.254 (talk) 21:17, 1 November 2010 (UTC)

What is the average age of onset of Alzheimer's disease?

Abdbdba (talk) 22:10, 30 October 2010 (UTC)
Wikipedia has an article on Alzheimer's disease and its section Epidemiology is what we can offer. Note that "onset" of Alzheimer's disease is hard to quantify. The data is for diagnosed cases. Cuddlyable3 (talk) 22:33, 30 October 2010 (UTC)

I couldn't see an average age of onset in that section. DuncanHill (talk) 22:35, 30 October 2010 (UTC)

Wikipedia also has an article about Early-onset Alzheimer's disease which notes that the majority of sufferers are in their 50's, or early 60's.Cuddlyable3 (talk) 22:46, 30 October 2010 (UTC)

SECIS element

The SECIS element causes UGA stop codons to encode selenocysteine instead of stopping translation. But if it occurs in the 3' untranslated region of the mRNA in eukaryots, how does it effect this change in translation? If it binds to the ribosome in some way, couldn't the SECIS element bind to a ribosome while it is translating a totally different mRNA? Icek (talk) 22:40, 30 October 2010 (UTC)

The present article is woefully incomplete. From [5] it appears that what SECIS binds is still being investigated, though some proteins are known; in fact it appears different SECIS binding elements will interact with different "spectrums" of proteins. (In reality what that means is that the authors found that SECIS elements bind nucleolin with widely varying affinity, but then again, they don't know where nucleolin binds it) Also see SECISBP2.

The present guess from the above article (which may not cover all ideas) is that the SECIS element leads indirectly to the binding of the elongation factor and thereby holds the SeC tRNA in the general neighborhood of the ribosome while the SECIS-containing mRNA is attached. Alternatively they suggest there might be a different initiation event from the 5' end ... I can't say exactly how that leads to recruitment of the SeC tRNA. Wnt (talk) 21:11, 31 October 2010 (UTC)

does citric acid actively mask the taste of ethanol?

It's well-known that citrusy fruit (lime, oranges, etc.) will mask the taste of alcohol, but I see none of our biochemistry articles cover this phenomenon. At what level does the masking occur?

Does it occur at the nervous system level (i.e. citrus reception inhibits ethanol bitterness signals?) or the receptor-chemistry level (citric acid binds competitively to ethanol receptors, or ethanol's affinity for ethanol receptors is downgraded by citric acid?). Is it ionic citrate or the neutral citric acid that does the masking? John Riemann Soong (talk) 22:53, 30 October 2010 (UTC)

From my perspective, almost anything (except water) added to alcohol masks (changes) its taste. I've never heard (to contrast with your contention that it is "well known") that "citrusy fruit" did a more pronounced job than, say, cola. As for how any soda or fruit juice effects such a change is a question I will leave to the scientists here. Bielle (talk) 23:32, 30 October 2010 (UTC)

Cola doesn't mask it really well -- it simply dilutes or masks it with the taste of sugar (which isn't that good of a masker). I take it there's a reason that "hard lemonade" and adding lime to drinks are popular practices. John Riemann Soong (talk) 00:20, 31 October 2010 (UTC)

Taste and smell receptors are limited in variety. It does not seem unlikely that those which are sensitive to one kind of solvent (alcohol) might be limited by another (acid). Ginger Conspiracy (talk) 03:43, 31 October 2010 (UTC)

I do not know their full diversity, but as I recall, taste receptors have to number several dozen in type, and smell receptors several hundred. (The "five taste" model is vastly oversimplified of course.) John Riemann Soong (talk) 04:53, 31 October 2010 (UTC)

Taste receptor mentions 25. 75.41.110.200 (talk) 05:47, 2 November 2010 (UTC)

Difficulty in differentiating actors and actresses from the fictional characters they portray?

Is there a specific term for this? Not necessarily in the creepy, obsessional way (though it could be the same thing) but more along the lines of when fans of long-running dramas and soap operas approach the actors and actresses when they see them in the street and talk to them as though they were the same person as the character they play in the show, refer to them by the character's name, etc. Sometimes when you read interviews with the actors, they tell stories about 'this guy/woman who came up to me this time and...'. Things like people who play doctors being asked for medical advice, or being dragged over to help because someone is having a heart attack/seizure/baby - or actors and actresses being insulted or threatened by members of the public for the actions of their characters (say if the character was a rapist, or murderer, or wife-beater), or being praised for being strong enough to overcome rape/wife-beating/cancer/grievous injury - or actors in sci-fi shows being asked questions as though the fictional universe of the show was real, etc... --Kurt Shaped Box (talk) 23:19, 30 October 2010 (UTC)

Are you describing an extreme case of typecasting (acting)? -- 119.31.121.89 (talk) 00:29, 31 October 2010 (UTC)

That is the word, but it's actually less extreme. Just having a few audience members confuse an actor or actress with a character is far better than when casting decision makers start doing it. That could be why casting professionals are often been kept separate by studios from producers and directors. By the way, this question would probably get a better answer on WP:RDH the humanities reference desk, because the theatrical branch of forensics (public speaking) is an art, not a science. Ginger Conspiracy (talk) 03:52, 31 October 2010 (UTC)

I'm no psychology expert, but it seems to be almost a type of Transference. --jjron (talk) 03:55, 31 October 2010 (UTC)

Perhaps some fans think that the best way to interact with an actor is by acting? It's hard to say how people decide on their self-amusements. Wnt (talk) 20:55, 31 October 2010 (UTC)

Theory?

I can remember seeing a program on teleportation. One (of the many) drawbacks of teleportation was that some theory said it was impossible to know the exact position of every sub-atomic particle all the time. What's the theory called? Albacore (talk) 23:57, 30 October 2010 (UTC)

The Heisenberg uncertainty principle indicates that we may know the exact position of a subatomic particle, or the speed at which it is moving, not both. (This also applies on the macro level; you can know the location of e.g. a car, or its speed, but cannot discern both at the same time, as speed is dependent on knowing the car's position in at least two places and calculating how fast it got from one to the next.) → ROUX ₪ 00:00, 31 October 2010 (UTC)

I often find myself driving around in my car and knowing both where I am and how fast I am going both at the same time (and I've noticed that even more since the advent of GPS navigation technology). WikiDao ☯ (talk) 00:08, 31 October 2010 (UTC)

In that case, it is actually two different observers. Your odometer is observing your speed (and does not know your location), while your GPS knows your location (but not your speed). → ROUX ₪ 00:11, 31 October 2010 (UTC)

(I'm not often aware of my momentum and my location at the same time, though, it's true). WikiDao ☯ (talk) 00:13, 31 October 2010 (UTC)

(In practice, your GPS can figure out your speed pretty easily. I think it is probably known on here — but worth stating for such a basic question — that HUP only applies to very small scales, e.g. things smaller than atoms. --Mr.98 (talk) 00:14, 31 October 2010 (UTC))

There is some uncertainty for an object the size of my car, though, right? It's just that it is indistinguishable from zero because of the value of ħ in

$\Delta x\,\Delta p\geq {\frac {\hbar }{2}}$

if I recall the explanation for that correctly. Is that right, or what is a better way to understand that? WikiDao ☯ (talk) 01:07, 31 October 2010 (UTC)

Exactly right:

$\Delta x\,\Delta p=\Delta x\,\Delta v\,m\geq {\frac {\hbar }{2}}\approx {\frac {1}{2}}\cdot 10^{-34}\mathrm {J\cdot s} =10^{-17}\mathrm {m} \cdot 10^{-17}\mathrm {m\cdot s^{-1}} \cdot {\frac {1}{2}}\mathrm {kg}$

and you are not able to measure the velocity of even a half kilo particle with an accuracy of 10^-17 m/s nor its position with an accuracy of 10^-17 m. -- 124.157.254.112 (talk) 04:54, 31 October 2010 (UTC)

Oops -- just reedited the equation as I had dropped the 2. -- 124.157.254.112 (talk) 05:09, 31 October 2010 (UTC)

I wasn't trying to imply you couldn't calculate HUP for your car — just that it was so small as to be meaningless on a macroscopic scale, and thus the car's position/momentum could easily be treated classically for really all but the most silly purposes. --Mr.98 (talk) 15:36, 31 October 2010 (UTC)

Yes, I understood that you understood that, 98. I only brought up driving around in my car because Roux brought up macro-world "uncertainty", and the above really needed to be said here after that, because it was very misleading imho... WikiDao ☯ (talk) 23:11, 31 October 2010 (UTC)

No it wasn't. I was attempting to explain the principle in real world terms. Obviously for everyday life HUP doesn't apply to the macro world. But in a very specific sense, it does. Whatever. → ROUX ₪ 23:14, 31 October 2010 (UTC)

As far as the uncertainty principle is concerned, it doesn't matter if there are two different observers; it only matters what information is measured, not who knows it. (And GPS devices do measure your velocity.) I'm not sure if plugging the mass of your car into ΔxΔp ≥ ħ/2 makes sense. Quantum behavior only shows up in systems that are thermally isolated, which a car certainly is not. Emitting blackbody radiation is effectively the same as being measured. It might make more sense to plug in the mass of the "car plus environment" (leading to even less practical uncertainty), but I'm not sure how big that environment would be.

Going back to the original question, there are a lot of reasons why teleportation is impossible, but the uncertainty principle is not one of those reasons. It is potentially a problem if you encode your vital statistics as classical bits, but you don't have to do that; you can use qubits. If you manage to solve all of the other unsolvable problems of teleportation, quantum computing hardware should be child's play. -- BenRG (talk) 06:49, 31 October 2010 (UTC)