Wikipedia:Reference desk/Archives/Science/2011 January 10

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January 10

Single Photon/Electron emision.

Articles showing the wave/particle duality of electrons and maybe photons demonstrate aiming individual particles at slits with a resultant interference pattern.However they never explain how single particles are produced and aimed(especially a photon which I assume cannot be magnetically influenced). John Cowell. 118.208.9.92 (talk) 00:59, 10 January 2011 (UTC)

Double-slit_experiment#Quantum_version_of_experiment has a description of such an experiment with single (Fock state) photons and has a few references. You could, presumably, follow the references for more details. --Jayron32 01:04, 10 January 2011 (UTC)

Thanks for reference,(though the maths was beyond me) ,the articles did not explain how to produce,aim and fire the particles from an engineering standpoint. John Cowell. 01:36, 10 January 2011 (UTC) —Preceding unsigned comment added by 118.208.9.92 (talk)

Presumably this: [1] reference (from the article) would be at that level of detail. If not, it itself would have references you could follow to earlier descriptions of such methods. --Jayron32 01:56, 10 January 2011 (UTC)

Laser and polarization filter

All the photons in a laser are entangled together, right? Does that mean that if one of the photons passes through a polarization filter, the rest will as well? In other words, do they always either let all or none of the light through? — DanielLC 03:17, 10 January 2011 (UTC)

No, all the photons in a laser are not entangled. And if you had a beam of entangled photons, just because one went through a polarization filer does not mean all of them do. And finally if you did send all the photons in a beam of entangled photons through a polarization filter it does not mean all or none - quite the opposite, some will go through, some won't, and some will end up in sort of a partial state of going though and not going though. But in total, half will end up going through and half won't. Additionally a polarization filter is (one) method of creating entangled photons in the first place. Ariel. (talk) 09:20, 10 January 2011 (UTC)

Some kinds of lasers do produce linearly polarized light, but semiconductor lasers and gas lasers without polarizing Brewster windows do not. 71.198.176.22 (talk) 15:20, 10 January 2011 (UTC)

Actually, many semiconductor lasers do produce polarized light. The waveguide in the semiconductor is not rotationally symmetric, and somehow this induces polarized lasing.--Srleffler (talk) 06:24, 15 January 2011 (UTC)

Zero Transit Time

In days of yore we were told that atoms had a nucleus with electrons "orbiting" at a relatively large distance away.In an airforce avionics lecture we were taught that electrons changed orbit/energy levels/shells/fuzzy balls/etc emitting or gaining energy depending on circumstance and this involved travelling a very small but finite distance in zero time.I feel a warpdrive coming on! John Cowell.04:10, 10 January 2011 (UTC) —Preceding unsigned comment added by 118.208.9.92 (talk)

They were wrong. The evolution of a quantum system, such as an electron, can be calculated with the Schrödinger equation. It is not instantaneous. — DanielLC 04:15, 10 January 2011 (UTC)

They were not entirely wrong. See de Broglie wave. *gets popcorn* 71.198.176.22 (talk) 15:14, 10 January 2011 (UTC)

I've not seen anywhere that de Broglie waves aren't limited by the same physical laws as the objects that are associated with them? --Jayron32 16:53, 10 January 2011 (UTC)

An electron occupying an atomic orbital is in a de Broglie wave more properly associated with a probability distribution than a point, even considered as a solution to the Schroedinger equation. Therefore it can be said to be occupying disjoint space simultaneously whereas a more point-like nucleus can not, until several orders of magnitude smaller distances are considered. 71.198.176.22 (talk) 17:28, 10 January 2011 (UTC)

Yeah, but that doesn't mean the electron "jumps" magically between different points instantly; it just means that a single electron is "smeared out" over a certain volume of space; it is partially and simultaneously in multiple locations. --Jayron32 19:29, 10 January 2011 (UTC)

Guys, this is easy. Apply Heisenberg's uncertainty relation. Whether the jump is instantaneous or not is irrelevant, because we can't measure it instantaneously. Any change of the quantum state ΔE is accompanied by a characteristic Δt. Specifically, the change in electron energy follows the relations laid out in this section; the more "resolution" you want on the energy scale, (in other words, if you want to measure a single quantum of energy), the more time your measurement necessarily gets smeared out over. Nimur (talk) 22:52, 10 January 2011 (UTC)

Motor oil leakage in cold weather

I bought my car knowing that it had some problems; among these is a slow oil leak. I've been advised that a repair job might be difficult (no clue where the leak is, for example) and that it's not at all necessary, so I take care of the situation by checking the oil regularly and adding more when necessary. As we've descended into the North American winter, I've noticed that the oil level changes less between times that I check it, even though I don't think to check it as frequently. Is there any chance that the cold weather reduces the rate at which the oil leaks? Please note that the rate at which I was losing oil before, while not great, was far faster than could be accounted for by the oil that I wipe off the dipstick when I check it. Nyttend (talk) 04:20, 10 January 2011 (UTC)

Motor oil (see article) may increase Viscosity at low temperature, especially if it is not fresh, which could explain the slower leak. Your real problem is to locate the leak so is a web page that can help[2]. Warning: Are you sure it is only motor oil leaking? A leak of brake or transmission fluid is a serious fault that needs immediate attention. Cuddlyable3 (talk) 04:54, 10 January 2011 (UTC)

With modern multigrade motor oils the viscosity shouldn't change that much. Maybe one of the rubber seals is stiffer? Or the cold is causing parts to shrink a bit tightening the gap? Or it could simply be self-sealing (i.e. gunk is blocking the hole) - you won't know till summer. Ariel. (talk) 05:49, 10 January 2011 (UTC)

Cuddlyable — I know that it's motor oil, because the levels on the engine oil dipstick go down (or went down) from week to week. Nyttend (talk) 23:19, 10 January 2011 (UTC)

Does the skull grow at the Sutures?

A regular bone grows from the ends, which eventually fuse. What about the skull? Does it grow from the Sutures? Ariel. (talk) 06:27, 10 January 2011 (UTC)

The flat bones of the skull and face form via intramembranous ossification which is distinct from endochondral ossification (the typical way that long bones grow via the growth plate). This is also discussed briefly in Bone#Formation. The bottom line is that the sutures are where the skull bones fuse together but not where the growth originates. --- Medical geneticist (talk) 11:23, 10 January 2011 (UTC)

electricity through eco friendly means

dear sir,
i have an idea of to produce electricity by using mechanical energy that is produced when a cycle wheel rotates so what are the apparatus to be used and the design and the important thing is that it should be a low cost model —Preceding unsigned comment added by 117.204.69.78 (talk) 09:05, 10 January 2011 (UTC)

I think you mean a generator. But the hard part (meaning the expensive part) is not producing electricity, the hard part is producing the mechanical energy. How are you going to make the mechanical energy? Ariel. (talk) 09:09, 10 January 2011 (UTC)

If you mean a bicycle wheel, I think technically it's an AC magneto, but they're always called dynamos, at least in the UK. They are available quite cheaply, but they don't produce a lot of electricity. See bicycle lighting.--Shantavira|^{feed me} 10:07, 10 January 2011 (UTC)

THe big problem with them is that your lights go out when you stop pedalling. Not terribly safe on a country road. Alansplodge (talk) 13:18, 10 January 2011 (UTC)

There was a TV programme in the UK a year ago in which a team of cyclists tried to power an ordinary house by this method. Their success was limited. Dbfirs 13:26, 10 January 2011 (UTC)

It should be noted that this is only as eco-friendly as your diet and lifestyle. Using beasts of burden (human beings, in this case) is not a very efficient or a priori eco-friendly way to utilize mechanical energy. --Mr.98 (talk) 14:10, 10 January 2011 (UTC)

http://mae.ucdavis.edu/~biosport/jkm/ped_desk.htm 71.198.176.22 (talk) 14:46, 10 January 2011 (UTC)

Presented only as information, and not a suggestion that anyone should undertake the experiment: It would be possible to generate a respectable amount of electric power with a stationary bike. A single bike alternator only produces a small amount of electricity, with more output voltage at higher speed. It is only designed to power the headlight and taillight of the bicycle, putting out only 6 watts or so. Their efficiency is only 70% or so, per Bicycle lighting. One might collect several old bicycle alternators, and mount them on the bike frame so they can be placed in normal contact with the rear tire. One could connect a bridge rectifier to each one to produce DC electricity. Various connections could produce 12 volts DC to power a battery charger. An inverter connected to the 12 volt battery could power small appliances such as a small TV. Peddle like hell, so that you are producing a small fraction of a horsepower of mechanical energy. I would not expect more than 60 watts of output for an extended period if I were peddling such a bike generator. Some experimenters have gone a step beyond and connected a stationary bike to a salvaged 12 volt car alternator, perhaps via a v belt rather than the low efficiency connection of a bike alternator rubbing on the tire. The alternator might be able to put out 100 watts, depending on the model used, but the human power source might limit the long-term output. Edison (talk) 03:23, 11 January 2011 (UTC)

If the stationary bike I use is accurate, it really is not all that difficult for a reasonably in shape human to produce 150 watts of power for 30 min. If you want more then that, you might want to see if Lance Armstrong is busy. Googlemeister (talk) 14:22, 11 January 2011 (UTC)

Engineering

how can we make rotation of fan reverse? — Preceding unsigned comment added by Hk wk (talk • contribs) 11:22, 10 January 2011 (UTC)

An electric fan? If so, reverse polarity of the power source. -- kainaw™ 14:05, 10 January 2011 (UTC)

If you merely reverse the polarity of the single phase AC power supply to an electric fan, it will still rotate in the same direction. Consider the phase relation of the armature and field, to find a way to reverse it. If it had a three phase power supply and motor, switching any two of the supply connections would cause it to rotate in the reverse direction. Edison (talk) 03:06, 11 January 2011 (UTC)

Or simply turn it round to face in the opposite direction. Whether reversing the polarity at the power source will work depends on the design.--Shantavira|^{feed me} 14:12, 10 January 2011 (UTC)

It depends on the kind of motor it has. You'll probably have to open it and change wiring. A D/C fan can be reversed by changing the polarity. A/C fans are more complicated and it depends on the exact type. Ariel. (talk) 20:21, 10 January 2011 (UTC)

Warning: Remember that electricity can kill. If the fan is powered by a 12-volt battery, "opening it and changing wiring" is probably fairly safe. If it's a mains-powered fan, don't risk your life trying it. Mitch Ames (talk) 13:39, 11 January 2011 (UTC)

I don't think Ariel was saying to open it while the thing is running. Googlemeister (talk) 14:20, 11 January 2011 (UTC)

AC power doesn't have a "polarity" of course, just one terminal that has a higher potential with respect to the earth, so there is no point in reversing the incoming wires in a fan that runs on mains electricity (unless it happens to be an enormous 3-phase industrial fan as mentioned above). Altering the internal circuitry might work on some AC motors, but should only be attempted by a professional who understands the circuitry. For a DC motor, there is no need to open anything to reverse the motion, just change the polarity at the source. In either case, best safety advice is don't open it. Dbfirs 17:06, 11 January 2011 (UTC)

Hiding gold in ink

In the Mr. Monk Gets Married episode of the popular television series, the secret hoard of gold is found to be in the ink of a prospector's journals. Monk says that the prospector had melted down the gold and mixed in black ink, and that "any amateur chemist could do it". Now, I have my doubts - I would expect the ink to evaporate explosively on coming into contact with the molten gold (at over 1000°C). So - is there a way in which an amateur chemist could have hidden his gold in ink? DuncanHill (talk) 11:59, 10 January 2011 (UTC)

Gold paint can be made with powdered gold. I'm not sure of the technical difference between paint and ink, but it could take several volumes of writing to use up one ounce of ink, so I can't see how this would be practical way to conceal any appreciable quantity of gold.--Shantavira|^{feed me} 13:01, 10 January 2011 (UTC)

He did write a lot of journals. I should have mentioned that the ink needs to look like ink and not like gold, as the purpose was concealement. DuncanHill (talk) 13:07, 10 January 2011 (UTC)

I haven't tried this, but it might work with finely powdered gold and high-carbon ink because the gold powder would tend to sink under the layer of carbon. This would not be a very practical method because the concentration would need to be low to conceal the gold. If Monk the prospector had the facility for melting gold, then casting it into an everyday object and painting it to match would be a better option, though care would need to be taken that the object could not be "lifted" (in either sense). Dbfirs 13:21, 10 January 2011 (UTC)

Monk found the gold, it was the prospector who hid it. DuncanHill (talk) 13:25, 10 January 2011 (UTC)

Sorry, I should have read your post more carefully. How did Monk find it? Dbfirs 13:29, 10 January 2011 (UTC)

He had a clue! The prospector had let it be known that his gold could be found in his journals, so everyone assumed you had to read the journals, which Monk started to do. However, they were full of inconsequential ramblings, and eventually Monk realised that the volumes were very heavy, and he realised that the gold was literally in the journals. DuncanHill (talk) 13:32, 10 January 2011 (UTC)

Gold(III) chloride is a green liquid that can be mixed with ink. What one need to avoid however, is anything which will cause the gold to precipitate out as metal. Also, it is a salt and will corrode your nib. --Aspro (talk) 13:48, 10 January 2011 (UTC)

The journals were discernibly heavy? Think of how little ink goes onto a page compared to the weight of the page. Even if the ink was ten times heavier (gold instead of carbon), would you be able to notice the difference between a journal and a journal with writing on? APL (talk) 21:27, 10 January 2011 (UTC)

The weight must have been increased by at least 7000 ounces of gold, even at today's prices. That's a lot of ink to hide so much gold! Dbfirs 11:01, 11 January 2011 (UTC)

It's a television gimmick... --Mr.98 (talk) 23:07, 10 January 2011 (UTC)

Why did Alorica close its office in Manhattan, KS?

I tried Googling for it; no straight answers. Also, I called the WORLD HEADQUARTERS of it in Chino, and the lady who answered didn't know either. Does anyone know? Is there a supergoogle they can use to figure out why Alorica closed its doors in Manhattan? Thanks. --70.179.178.5 (talk) 12:22, 10 January 2011 (UTC)

This isn't really a science question. Alorica appears to be a privately owned corporation, which means that (in the United States), the corporation is not required to disclose anything about their business and financial decisions. If they want to close an office, or set fire to a pile of cash, they aren't really accountable to anyone over it. Nimur (talk) 22:58, 10 January 2011 (UTC)

If I get homeless but still have my Dell Inspiron 1720 laptop, how do I make money online with little/no overhead?

My laptop has been all paid off. It was manufactured in Fall 2007 so thanks to the rapidly-depreciating nature of these devices, hardly anyone should think it's worth stealing. (I'd still use a Kensington lock on it.)

So let's say I find a 24-hour coffee shop to camp out in, since I probably might not have much of a choice. I may still have my debit card that I have now, so I could still get started somehow.

However, I might not have all that much money in the first place, so on this laptop, how do I get started on a very low-overhead online business, in order to get back on my feet and earn a living again? What ideas do you have in regards to that? (Ebay's out of the question; when much of my possessions would already be gone, there isn't much to sell on there. Besides, their fees are the highest of any auction site and I'm only allowed to sell up to 100 items/$5,000 a month. I need to be able to make money without physically possessing much.) --70.179.178.5 (talk) 12:29, 10 January 2011 (UTC)

I can't really help because I had the same idea when I was living on an income below the poverty line, but I didn't find any good money-making schemes. My reason for replying is just to warn you to beware because most of the "money-making schemes" are really just scams designed to defraud you either by asking for money up-front or by paying ridiculously low rates of pay. I hope you have more success than I did, and I hope you don't end up homeless. Is there no ordinary work available in Compton? Dbfirs 12:43, 10 January 2011 (UTC)

What he said. If there were straightforward and reliable ways to make an adequate living from a coffeeshop using only a laptop and their wireless internet connection, I suspect you'd see a lot more people doing so. Unless you can actually come up with a solid business plan for yourself and you have some particularly desirable (valuable!) skills that you will be able to market and use effectively over the Internet, then you're probably better off just getting a job working at the coffee shop. TenOfAllTrades(talk) 13:58, 10 January 2011 (UTC)

Proof-reading, translation, website design, marketing consultancy, but you have to have the necessary skills. Either use your existing contacts to drum up business or sign up with agencies. Itsmejudith (talk) 14:34, 10 January 2011 (UTC)

If you have to ask, then I really doubt if you have the entrepreneurial qualities to exploit the opportunities out there. For instance; you dismiss Ebay -why? You might not have stuff but you do have time on your hands and other people are always throwing away stuff and may even be willing to pay you to take it away, which you can then sell on Ebay. Via Ebay you can advertise your website (you do have a web site don't you) on which you can also advertise other peoples products and get another income stream (but this will be usually peanuts)(that said, the local cat-house might offer good rates of several dollars a click if you can show you are attracting lots of local traffic to your site). You can also use it to advertise your own personal services which you can do because of all that time on your hands. With time on your hands you can travel out and about -take a compact camera with you which can also record video. Keep an eye out for trouble and sell the footage to news channels. Even local papers might of a few dollars for a good action photo. Bank robberies in progress etc., you can syndicate world wide for bigger bucks. Upload to the studio immediately from the scene of the crime. If your out every day you will see these opportunities. Also, for every 20 local businesses you ask. about two will be willing to have a sort video advert posted on Youtube (taken with you camera – with your personal testimony voice-over that it is the kebab shop in Compton or whatever ). Again place links to your website (and their's of course) etc., etc. You have to work as hard at it, as any other job. Plan for being told NO! 25-30 times a day. The few that say 'yes' will more than make up for those that say no. Do lots of small cheap jobs and those bigger ones will just come along by themselves unexpectedly. Don't forget to put money aside for paying taxes.--Aspro (talk) 14:37, 10 January 2011 (UTC)

"Compton"? Two people mentioned Compton. The IP geolocates in Manhattan, Kansas. Keep an eye on Craigslist for your area. 71.198.176.22 (talk) 16:07, 10 January 2011 (UTC)

You can Turk. Its generally small amounts of money, but if you have time and select jobs wisely, you can make a reasonable amount of cash doing it. --Jayron32 16:09, 10 January 2011 (UTC)

But do not accept any jobs that offer payment for writing WP articles.--Aspro (talk) 16:25, 10 January 2011 (UTC)

A lot of web money-making opportunities are not simple things that you can turn on like a switch. For instance some blogs and webcomics are profitable, but only after years of slowly gaining a readership and a following. They're essentially creative businesses that have to be slowly built up from absolute zero. APL (talk) 17:49, 10 January 2011 (UTC)

I think the safest choice is to put all your energy into getting a normal job working 8 hours a day, and once you have landed that and thus secured the means of survival, in your spare time use the laptop to learn a computer-based marketable skill like web design or computer programming or database programming or 3D modeling or the like. Do whatever you can to network with like-minded professionals. After a year or two of such training, depending on how far you progress, you may have enough experience to build a decent portfolio and apply for jobs in a more lucrative field, thus beginning a career. Comet Tuttle (talk) 19:20, 10 January 2011 (UTC)

Agreed. Tech job stuff is high risk (and no benefits) even in better economies, and when one has resources to fall back upon. The best "no skills required" jobs I've seen lately are working at Whole Foods, which has excellent benefits plans and huge discounts on food. But really anything is better than trying to make money from your laptop when you have no home. (The "ghetto paparazzi" option of Aspro is perhaps the silliest one I've seen so far.) --Mr.98 (talk) 19:46, 10 January 2011 (UTC)

Isn't Kansas State University in Manhattan? (Or if you're not a fan, there's also Wichita State University; thousands of other universities exist in the US). Both universities have continuing education programs: KSU Admissions and WSU Office of Continuing Education. Even if you have no money, you may be eligible for scholarships or loans; a university degree will dramatically improve your marketability to employers. This is a much better long-term plan than trying to make money on a laptop, working out of a coffee shop. Nimur (talk) 00:01, 11 January 2011 (UTC)

Have you given up on your plans to emigrate to South Korea? Dbfirs 10:47, 11 January 2011 (UTC)

I don't think it's appropriate to assume that identical IPs means the same person. It could be a shared IP. 71.198.176.22 (talk) 20:32, 11 January 2011 (UTC)

Yes, it is a shared IP (from a previous questions), but the style seemed familiar and seemed to belong to the owner of the router. Apologies if I guessed wrongly. Dbfirs 07:46, 12 January 2011 (UTC)

If you want a lucrative job that can be performed in a cafe, just write the next hyper-successful work of popular fiction. --Anonymous, 06:59 UTC, 1/11/11 (or 11/1/11, or...).

I don't know if this is useful to you, but if you have some writing or coding skill there are sites like elance.com and guru.com that will pay rather low rates for such work. Wnt (talk) 14:03, 13 January 2011 (UTC)

Cheapest source of ethanol for sterlisation

A while ago, I asked where is the cheapest place for ethanol (for sterilisation) in the UK and it now seems to me that we already have a reasonably-priced source, compared to alternatives that I've checked. The cost is £6.60 for 2.5 L analytical grade (100%), or £2.64/L. How much do you pay per litre at your laboratory? ----Seans Potato Business 15:40, 10 January 2011 (UTC)

My laboratory buys ethanol for colloquia when there's a VIP presentation or someone just managed a big grant, not sterilization. Try asking at http://www.chemicalforums.com/index.php?board=19.0 instead. 71.198.176.22 (talk) 07:24, 12 January 2011 (UTC)

Linearization

Hi! I have to linearize a hyperbolic graph. Data: x:1,2,3,4,5,6,7,8 y:8,1;4,7;3,1;2,0;1,4;1,0;0,7;0,5. I've already squared x bu got a hyperbola again. Please help. — Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 18:02, 10 January 2011 (UTC)

Have you tried taking the inverse or the inverse square or the inverse cube of the data? --Jayron32 19:25, 10 January 2011 (UTC)

Do you want an equation for a linear approximation for this graph? You can use Microsoft Excel to construct a linearization for you; here are instructions from Purdue University and from the official Microsoft Office help page. A linear least-squares fit from Microsoft Excel produced y = -0.9536x + 6.9786 with an R² of 0.8 (in other words, not a very good fit - but hyperbolae aren't linear! So this poor fit is not unexpected). Knowing something about your purposes would help us pick a better methodology; you can linearize with other techniques than least squares; I would vote for a tangent-line at x=5 or x=6 value; or a set of two linear segments to account for the "steep part" and "shallow part". You could also linearize the logarithm of your hyperbola. Nimur (talk) 23:16, 10 January 2011 (UTC)

Oh, I thought he was trying to derive the best-fit equation to the hyperbola using the linear method. You can often do so by brute force; if you do stuff like square or take the inverse or take the natural logatithms or some combination thereof, and replot the data, if the manipulated data is linear you can back-derive the best-fit equation for your original data. Its a common method used in deriving the Rate equation in chemical kinetics, the integrated rate law is manipulated and plotted to see if the graph is linear; if it is the order of the original rate law can be determined. --Jayron32 23:56, 10 January 2011 (UTC)

frost on windows of vehicles

why does frost form on my cars windshield when parked outside my carport, but none when parked inside? —Preceding unsigned comment added by 72.45.79.233 (talk) 19:37, 10 January 2011 (UTC)

It is dew from the air that sort of "rains" down on it. In a carport there is little air, and so, little dew. Ariel. (talk) 20:20, 10 January 2011 (UTC)

Frost may also form without any intermediate liquid form; it may form via deposition. But broadly speaking, the relative humidity still controls when and where frost will form. --Jayron32 20:33, 10 January 2011 (UTC)

Those responses are correct but they leave out an important factor. A solid object exposed to the sky on a clear night will lose a lot of heat by radiating to space -- the result is that things like cars can become a lot colder than the surrounding air. If there is a cover over the object, it radiates heat back, greatly reducing this effect. Even a cloud cover will considerably reduce radiative heat loss. Looie496 (talk) 20:59, 10 January 2011 (UTC)

This is the reason why you can make ice in the desert even if the air temperature stays above freezing, right? Do we have an article about that? SemanticMantis (talk) 23:38, 10 January 2011 (UTC)

We have an article on Radiative cooling but it could use some serious work. --Jayron32 23:51, 10 January 2011 (UTC)

MnCl2 formation

Why doesn't the reaction of various manganese salts such as manganese dioxide or manganese carbonate with hydrochloric acid not make a light pink solution? The user here had the same result. --Chemicalinterest (talk) 20:40, 10 January 2011 (UTC)

• Mn and other transition metals form complexes with Cl rather than water. Graeme Bartlett (talk) 23:01, 10 January 2011 (UTC)
• Solutions of [Mn(H₂O)₆]²⁺ in water are pretty much colourless to the naked eye, at least all the ones I've seen. You can see the pink colour in the solid because the solid is more "concentrated". Physchim62 (talk) 00:19, 11 January 2011 (UTC)

It's not colorless; it is dark brown to black. --98.221.179.18 (talk) 17:54, 11 January 2011 (UTC)

Effective range for a buffer

The rule of thumb is that a buffer is effective in the range of plus or minus one pH unit from its pKa. Glycine has a pKa of 2.34, but I have seen some more or less reliable sources list its effective range as 2.2-3.6. Why would a buffer have a skewed effective range like this? ike9898 (talk) 21:52, 10 January 2011 (UTC)

Amino acids, being zwitterionic, are far more complicated. Also, you have not designated the complete buffer system. Are we talking about, say, a sodium glycinate/glycine system? An ammonium glycinate/glycine system? A glycinium chloride/glycine system? --Jayron32 22:04, 10 January 2011 (UTC)

I don't know about the terminology but I suppose it would be glycinium chloride/glycine (essentially a solution of glycine acidified to pH 2.2 with HCl). Does the presence of the amine group matter? The proportion of these groups that are protonated won't change appreciably between, say pH2 and pH3. ike9898 (talk) 14:28, 11 January 2011 (UTC)

I think part of the issue is that the "+/- 1 pH unit from the pKa" is a rule of thumb that works best, like all chemical systems, in simple situations where there isn't a lot of factors to consider. I am just speculating here, but the deal with glycine is likely some sort of hydrogen bonding effects whereby the effective pKa of the glycine in buffer is slightly different than the actual pKa of glycine as measured by other methods. I did find this source which lists the same effective range you did, but I do not know what methods they used to arrive at that range. --Jayron32 16:00, 11 January 2011 (UTC)

The term "critical mass" in relation to repopulation

Is "Critical Mass", as a term to describe the number of a population in a natural environment, that would be needed to repopulate itself, actually used as such in science?

From The Last Day of the Dinosaurs :In order to survive, any species needs to maintain a critical mass of population. If it falls below that threshold, then there is no way to climb back from certain extinction. 99.237.87.79 (talk) 22:31, 10 January 2011 (UTC)

Minimum viable population gives some numbers, as does population bottleneck. -- Finlay McWalter ☻ Talk 22:41, 10 January 2011 (UTC)

Google Book-ing the terms "critical mass population extinction" brings up a few examples of the term being used in this context, but it seems to be used as a metaphor for the physics term, not a normally used one in ecology. This is probably because, as Findlay indicates, there are alternative terms that are more precise. The MVP is more complicated than a simple repopulation issue, no doubt because there are more factors involved for actual animal populations, and because unlike fissioning nuclei, there are inbreeding issues to take into account. --Mr.98 (talk) 22:58, 10 January 2011 (UTC)

Small populations have decreased per-capita growth rates due to Allee effects. In sexually reproducing animal populations, Allee effects can arise from problems finding mates once the population drops below a critical threshold. As others point out, 'critical mass' is not a phrase commonly used by ecologists. SemanticMantis (talk) 23:45, 10 January 2011 (UTC)

"Allee threshold", or extinction threshold describes the point at which growth rates change from positive to negative, suggesting persistence or extinction, respectively. See e.g. [3] SemanticMantis (talk) 23:52, 10 January 2011 (UTC)