Science desk
< January 31	<< Jan \| February \| Mar >>	February 2 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 1

Levitation material

Back in the mid 80's, I recall that a group (probably some university students) had mixed some compounds together which was then shaped into a disk. As I remember it, I believed that they needed to heat this compound in a kiln as part of the process. Later, they were then able to have this disk suspend over some sort of gas, perhaps liquid nitrogen or it could have possible have even been dry ice - I am not sure. It became an interesting science fair project and was repeated often (certainly at that time). Other than being able to get the compound to suspend or levitate - I can not recall what use it may have eventually became of it. Certainly, ideas of high speed trains utilizing this discovery were at the forefront. I do recall however that Omni magazine had a contest which was to determine the best practical use of this discovery and challenged its readers to submit idea/designs towards that end. Would anyone recall what I am referring to and how the Omni contest turned out?24.89.210.71 (talk) 02:24, 1 February 2011 (UTC)[reply]

The only thing that comes to mind for me is the Meissner effect. --Mr.98 (talk) 02:35, 1 February 2011 (UTC)[reply]

I agree, a levitating superconductor seems like the best explanation. Ariel. (talk) 03:00, 1 February 2011 (UTC)[reply]

That is exactly right. To be more specific, high-temperature superconductivity was discovered in the mid 80s. Low temperature surperconductors had been known for many decades previous to that time. Dauto (talk) 03:12, 1 February 2011 (UTC)[reply]

It was probably a demonstration of a YBCO (yttrium barium copper oxide) superconductor. It's sometimes called 123 or Y123, both because of the ratio of its metal ingredients (1:2:3 Y:Ba:Cu) and because it's a straightforward synthesis (as easy as 1-2-3...). The raw ingredients are sintered at around a thousand degrees to make the final product; that would be the kiln step you remember. I don't have a reference for the Omni contest, but mayhaps you'll have more luck given the material name. TenOfAllTrades(talk) 03:54, 1 February 2011 (UTC)[reply]

Lockout Hasps

what r Lockout Hasps used 4 — Preceding unsigned comment added by Tommy35750 (talk • contribs) 03:15, 1 February 2011 (UTC)[reply]

Sounds like Lockout-Tagout. Note that many readers here do not speak English fluently and are not teenagers, so text-message-abbreviations are not a great way to communicate. DMacks (talk) 03:49, 1 February 2011 (UTC)[reply]

They are used for teaching how to hack the man in the middle attack in a classroom demonstration. One student uses a lockout hasp and padlock to safely lock a message in a box. He leaves. Another student comes in and sees a padlock on the box and agrees to place his lock on the box. He leaves. The original student returns and sees two locks, so removes his lock. He leaves. The second student returns and removes his lock to get the message. Secure, right? No. -- kainaw ™ 03:57, 1 February 2011 (UTC)[reply]

Something about igniting salt water with radio waves - our energy savior?

I heard or read long ago about an experimenter shooting radio waves at a beaker of salt water, therefore igniting it.

How come I haven't heard anything else? If igniting salt water produces more energy than what it takes to ignite it, then wouldn't that be our energy savior once and for all?

If it truly works as hoped, we could shut down all the dirty power plants and refit all motor vehicles to run on salt water instead. To expend salt water would be an EPIC civic duty because we might stem the tide of rising sea levels just from burning it off.

Moreover, the source of energy should be epically cheap. How much $ per gallon would salt water sell for?

Anyway, if the energy expenditure-to-energy generation ratio isn't efficient enough, why not improve the tools and methods to make the process more efficient?

^{PS: I wonder what the emissions would be, and if it'd be detrimental.} --70.179.181.251 (talk) 05:01, 1 February 2011 (UTC)[reply]

How do you get the energy to generate the radio waves? I'll give you a hint: It probably invoves burning something that is the compressed remains of dead algae... --Jayron32 05:05, 1 February 2011 (UTC)[reply]

(ec) That's a lot of wondering to do about something that is total nonsense. Looie496 (talk) 05:07, 1 February 2011 (UTC)[reply]

Could someone supply the chemical equation for the combustion of saltwater, or prove that it is utter nonsense? Edison (talk) 05:12, 1 February 2011 (UTC)[reply]

It isn't combustion. If you take wet salt (or molten salt, but wet salt is easier to obtain) not salt water, but rather slightly moisten salt, and blast the shit out of it with a powerful electric current, you will electrolyze it into sodium metal and chlorine gas. The deal is, their's more than enough ambient energy in the air to provide the activation energy to cause the sodium and chlorine to pretty much instantly re-react again, creating a rather impressive fireworks show. You get lots of brightly colored flames when you do it. If you have a carefully controlled set up, you can isolate the chlorine gas (it will form at the cathodic electrode) and prevent it from recombining with the sodium. But if you basicly just jam the leads from an stripped extension cord into a pile of wet salt, you get some pretty awesome flames. (note to kids: DO NOT DO THIS AT HOME). This isn't actually combustion per se, its just the tiny bit of sodium and chlorine gas you just formed via electrolysis reacting to reform the salt. --Jayron32 05:25, 1 February 2011 (UTC)[reply]

...and it should go without saying – though I'll say explicitly it here anyway – that the heat and light energy released by the recombination of the chlorine and sodium will never exceed the amount of electrical energy that you put in to separate them in the first place. (This will be true regardless of the energy source used, actually—there's nothing special about radio waves versus electric current.) If it were possible to extract additional energy from the process, it would be a perpetual motion machine of the first kind. If you prefer to think of it in terms of combustion, sodium chloride is just the 'ash' you get when you burn metallic sodium in a chlorine atmosphere; it's the waste product you get after you've extracted very nearly all the available chemical energy. TenOfAllTrades(talk) 14:04, 1 February 2011 (UTC)[reply]

See the video here. The relevant part starts about at about 1:20. But yes, as Jaron implies, it's bullcrap. Specifically, bullcrap that a bunch of ignorant reporters decided to pass off as news years ago. Someguy1221 (talk) 05:32, 1 February 2011 (UTC)[reply]

Getting arsenic out of water

How does one purify arsenic out of groundwater.--128.54.15.47 (talk) 06:07, 1 February 2011 (UTC)[reply]

With ion exchange. --T H F S W (T · C · E) 06:39, 1 February 2011 (UTC)[reply]

See Arsenic contamination of groundwater. The sourcing is terrible, but it will provide you some good terms to Google for. Also, see the books listed here. -- Mesoderm (talk) 07:01, 1 February 2011 (UTC)[reply]

OP here (probably a different IP though). Anyone know the cheapest option on filtering arsenic out? If so, know the cost? I'm trying to compile a budget for a project and it would be a great help.--128.54.224.231 (talk) 07:50, 1 February 2011 (UTC)[reply]

It really depends on the scale. For a small scale - for one or a few households - reverse osmosis would probably be the cheapest however disposal of the "filtrate" and used filter cartridges will be a serious concern. Roger (talk) 07:55, 1 February 2011 (UTC)[reply]

I'm trying to develop a proposal for rural Bangladesh so it can't be anything too complicated I imagine. Specifically I'm responsible for the budget. I'm thinking a community scale of sorts. Household can work too. I know this is an odd question.--128.54.224.231 (talk) 08:02, 1 February 2011 (UTC)[reply]

I'd consider asking an expert at a school of public health, like Allan Smith at Cal Berkeley. Researchers at schools of public health usually have their heart in the right place, and will certainly know the data and many of the options. Looks like Bangladesh is on his list, too. -- Scray (talk) 12:55, 1 February 2011 (UTC)[reply]

Study what already works localy. [1]--Aspro (talk) 13:12, 1 February 2011 (UTC)[reply]

Planetary Satellites Book

Dear Wikipedia I emailed Dr. Burns at Cornell University (email redacted) and he does not think that Tidal Locking [2] timescale formula number 2 is in the book "Planetary Satellites." It is not in the Gladman article http://audiophile.tam.cornell.edu/randpdf/gladman.pdf. Formula 2 has 10 to the 10 years at the end of it. Would Professor Peale at University of California Santa Barbara (email redacted) who wrote the chapter have the answer?PaulNethercott (talk) 09:28, 1 February 2011 (UTC)[reply]

The answer to what? And how should we know whether some particular person can answer whatever? This is an encyclopedia, not an oracle. –Henning Makholm (talk) 10:04, 1 February 2011 (UTC)[reply]

A discussion about the formulae quoted in the article Tidal locking was started here and should be continued on the article talk page. The OP seems to have investigated the reference sources (no. 4) quoted in the article. To investigate further, one can look through the article history to find who has edited the article and try contacting them on their talk pages. Cuddlyable3 (talk) 11:38, 1 February 2011 (UTC)[reply]

Please don't repeat your question here after only 2 days. Cuddlyable3 (talk) 21:41, 1 February 2011 (UTC)[reply]

Using lasers to melt snow

Anything like this exist yet? ScienceApe (talk) 15:20, 1 February 2011 (UTC)[reply]

Why would you want to? A hair drier is likely to be more efficient than a laser would be for that purpose... --Jayron32 15:26, 1 February 2011 (UTC)[reply]

Possibly, unless it actually isn't very good at melting snow. Doesn't seem like it would require that much technological know how, so why don't we have these? Well I mean a device that blows hot air for the sole purpose of melting snow I mean. ScienceApe (talk) 15:36, 1 February 2011 (UTC)[reply]

Because melting snow requires a lot more energy than shoveling it out of the way. --Stephan Schulz (talk) 15:44, 1 February 2011 (UTC)[reply]

For roads maybe, but I had drive ways in mind mostly. ScienceApe (talk) 17:53, 1 February 2011 (UTC)[reply]

Why would there be a difference? --Stephan Schulz (talk) 17:56, 1 February 2011 (UTC)[reply]

Because on a driveway, you're breaking your back to shovel it! You're not using a truck. ScienceApe (talk) 18:10, 1 February 2011 (UTC)[reply]

This [3] doesn't use lasers, but it apparently uses a dragon. Acroterion _(talk) 15:50, 1 February 2011 (UTC)[reply]

As Acroterion say's. If you look at the Enthalpy of fusion you will see that it take about 333 kJ of energy. One only needs about 4KJ to then bring it to boiling. In other words, melting ice consumes a lot of energy , almost as much as boiling it. Might be cheaper to compress it, load it onto a bulk-carrier and sale it to Arabia. There exchange it for oil, which is costs less than bottled water.--Aspro (talk) 15:52, 1 February 2011 (UTC)[reply]

It's actually somewhat more efficient to collect the snow and melt it in a purpose-built device — just blowing hot air means wasting a lot of energy (not all of the heat is efficiently transferred to the snow; a lot of warm air would escape). See Winter service vehicle#Snow melter and Metromelt. In areas which receive sufficient snow, the only way to clear the roads can be to melt it in place and dispose of the runoff through the sewer system; there just isn't enough space available to store the snow locally, and carrying it long distances to the suburbs is cost-prohibitive. TenOfAllTrades(talk) 16:57, 1 February 2011 (UTC)[reply]

There is such a thing as a heated driveway, sidewalk, or roadway. Usually, it takes the form of a fluid heat-exchanger running through specially-constructed plumbing pipes underneath the pavement. This maximizes the energy-efficiency of the heat-transfer to the snow; heating from above with a "hair-dryer" or hot-air machine would result in huge losses to convection and warming the air. (Though, to call a heated driveway "energy-efficient" is being generous, at least). I have seen radiant heat lamps, but lasers, by their very nature, are extremely focused/collimated - so you'd be melting tiny millimeter-sized holes of snow at a time. If you had a special need, I imagine you could probably use a cutting laser, but there would be great potential risks of high-power reflections, in random directions, off the specular snow-surface. This would be an unpredictable and incredible safety hazard.Nimur (talk) 18:27, 1 February 2011 (UTC)[reply]

Well, the whole point is that, being a tightly focused beam of light, a laser is actually markedly worse for melting snow than just about anything, even the completely shitty hair-drier. The point wasn't that the hair drier would be a good idea, it was just that, as completely terrible a job as a hair drier would do, the laser would be even worse. --Jayron32 19:20, 1 February 2011 (UTC)[reply]

What's stopping you from adjusting the focus of the laser so it becomes more diffuse or focused? We have lasers that can do that. ScienceApe (talk) 19:48, 1 February 2011 (UTC)[reply]

Diffusing it reduces the power; if you make it wide enough to be effective, you reduce the heating power to the point where it becomes equally as ineffective. You can't get something for nothing. --Jayron32 19:51, 1 February 2011 (UTC)[reply]

I'm willing to bet that it's more efficient than a hair dryer though. ScienceApe (talk) 20:08, 1 February 2011 (UTC)[reply]

I doubt it. You know how snow is white? That means that it reflects optical light. In fact, the albedo of snow is about 0.9 - even if it's a little dirty. So almost 90% of the light intensity (that is, 90% of the energy) is wasted as reflected light. This says nothing of the energy loss in powering the laser - so we're talking about a process that is at best converting a small fraction of the input energy into thermal heating of snow. Nimur (talk) 20:53, 1 February 2011 (UTC)[reply]

That doesn't sound right... It's well known that mirrors don't work as armor against directed-energy weapons, I don't see how this would be different. Hell, if what you were saying is true, using snow to focus a diffuse laser might work better than a mirror. ScienceApe (talk) 21:19, 1 February 2011 (UTC)[reply]

Precision mirrors have reflection coefficients approaching 5 nines (99.999%). That would be a much higher albedo than snow. Energy reflected is, by definition, not absorbed as heat. A very tiny percentage of energy is absorbed by snow as heat; an even smaller percentage would be absorbed by a mirror. Whether such a small percentage of the incident energy is great enough to cause damage (or melt the snow) depends only on the quantity of incident radiation. A small percentage of a very large amount of incident energy may still be significant enough to heat, melt, or damage a substrate. But that doesn't make the process efficient. Nimur (talk) 23:51, 1 February 2011 (UTC)[reply]

Shining a laser pointer into the snow demonstrates how poorly this would work. The beam spreads out as soon as it hits the surface. The result is about a couple square inches of snow that's glowing p You'd need a very dangerous laser to melt the snow. APL (talk) 01:26, 2 February 2011 (UTC)[reply]

Even if that's true, there are other frequencies that can be used. The MTHEL uses infrared light. ScienceApe (talk) 02:30, 2 February 2011 (UTC)[reply]

That's great but how well is that frequency asborbed by snow? Or to put it a different way what's the frequency you intend to use and how efficient is the laser that makes it. Nil Einne (talk) 03:43, 2 February 2011 (UTC)[reply]

No idea, just saying that visible light is not the only frequency of light that can be used in a laser. ScienceApe (talk) 14:29, 2 February 2011 (UTC)[reply]

I think we all know that. It doesn't seem particularly useful in this discussion though unless you are actually proposing a frequency you feel can be used... Nil Einne (talk) 18:51, 2 February 2011 (UTC)[reply]

Actually I think it's very useful because the statement about snow reflecting 90% of a laser's light (assuming it is true) is not true at different frequencies of light. You can theoretically make a laser using any frequency so you can run the entire gamut of frequencies and state how much light is being reflected for each. ScienceApe (talk) 19:48, 2 February 2011 (UTC)[reply]

Er no one ever said any different??? Nil Einne (talk) 20:21, 4 February 2011 (UTC)[reply]

*facepalm* Now your comments aren't being particularly useful in this discussion. If someone says snow can reflect 90% of a laser's light, but it's not true for the entire range of frequencies, then it's disingenuous for me to simply let that statement go without challenging it because then people will believe that it is true for any laser when it's not. He may not have specified that it was, but if nothing else, I'm clarifying the information. ScienceApe (talk) 03:10, 5 February 2011 (UTC)[reply]

One practical consideration is that the small volume of tepid water produced by melting snow with a low-power heat source is much easier to deal with and dispose of than the much larger volume of super-heated steam that you will get if you flash boil the snow with a laser. Gandalf61 (talk) 20:01, 1 February 2011 (UTC)[reply]

What about flamethrowers, wiki's article says they were used to melt snow on JFK's inauguration. More efficient at removing snow? ScienceApe (talk) 20:16, 1 February 2011 (UTC)[reply]

More efficient then what? Lasers? Hair dryers? Vehicles that collect snow and melt it? Heated driveway/etc? Nil Einne (talk) 21:07, 1 February 2011 (UTC)[reply]

All of the above. ScienceApe (talk) 21:11, 1 February 2011 (UTC)[reply]

Have you heard of a device called a snowblower? APL (talk) 01:26, 2 February 2011 (UTC)[reply]

Yes I have, but I'm asking about more exotic methods of snow removal. ScienceApe (talk) 02:28, 2 February 2011 (UTC)[reply]

Lasers probably since as several people have pointed out they're a poor choice. At a random guess probably none of the others though. Nil Einne (talk) 03:41, 2 February 2011 (UTC)[reply]

Just sprinkle salt on the snow. Cuddlyable3 (talk) 20:35, 1 February 2011 (UTC)[reply]

That can be a less-than-ideal solution, especially for large scale applications. The salt doesn't disappear after the snow melts—it ends up in the soil (poisoning plants and nearby agricultural land); it makes its way down to groundwater (poisoning aquifers); it runs into nearby bodies of water (directly or through sewers, poisoning aquatic plant and animal life). It ends up damaging clothing and rusting automobiles. It corrodes iron rebar, damaging bridgeworks. Salt may need frequent reapplication if lots of snow is falling, and it becomes less effective as the mercury drops. (Below -18°C, sodium chloride brine freezes.) Salt's miserable stuff. TenOfAllTrades(talk) 20:46, 1 February 2011 (UTC)[reply]

You could perhaps think of building roads that have microwave emitters built into them... Count Iblis (talk) 01:32, 2 February 2011 (UTC)[reply]

Actually, the lasers have one point in their favor: conceivably, you could focus them on a very small faction of some ice on the ground, physically breaking it up so it could be pushed out of the way.

It makes me wonder, though: is there a way to make a microwave or more likely terahertz heating ray, calibrated so that it can pass straight through all snow and ice without absorption, but the moment it hits blacktop it is intensely absorbed, so that it creates a hot layer right at the surface of the driveway that physically severs the ice from the road? Terahertz has such complicated absorption spectra that I can readily believe several such frequencies exist. Once the ice is severed from the road, you run over it with some uneven roller or break it up with a heavy shovel, and slide it all aside. (for simple snow, you might do this twice, once to deliberately create a shell of ice at the road and the second to dislodge it, so that rafts of ice would make it easier to slide the snow out of the way)

I wish someone had implemented Meta:WikiPatents, which seemed an outstanding idea. The current system rewards only the people who are ready to plunk down $10,000 every time they think of some random idea like this, and everyone else just pays royalties. Wnt (talk) 02:13, 2 February 2011 (UTC)[reply]

This may be of interest: [4] 10draftsdeep (talk) 15:01, 2 February 2011 (UTC)[reply]

Laser dazzlers

The dazzler article has an unsourced mention of an "alleged use of a Soviet dazzler against a Space Shuttle in 1984". This seems very unlikely to me; how could this have been effected? And why? Googling the key terms turns up little more than Wikipedia forks and mirrors. Was this actually possible and where are these allegations?--Shantavira|^{feed me} 17:27, 1 February 2011 (UTC)[reply]

It was the Terra-3 complex that did it. The atmosphere straight up is very transparent - in other words, the laser power under goes little attenuation. More than enought to upset delicate sensors.--Aspro (talk) 18:12, 1 February 2011 (UTC)[reply]

Some discussion of this at Sary Shagan. Apparently the reason was just to bug the Americans, in response to Reagan's stubbornness on SDI. It's not the most brilliant thing to have done, but not out of character for the pre-Gorbachev USSR. Incidentally for years afterwards the US over-estimated the Soviet SDI work going on at Sary Shagan, which was in fact pretty primitive. Not sure if that's connected with this incident or not. --Mr.98 (talk) 18:34, 1 February 2011 (UTC)[reply]

Dreams

I saw this on a few blogs, but I can't find a source for it, is it true? "Fact: we only dream of what we know. Our dreams are frequently full of strangers who play out certain parts – did you know that your mind is not inventing those faces – they are real faces of real people that you have seen during your life but may not know or remember? The evil killer in your latest dream may be the guy who pumped petrol into your dad’s car when you were just a little kid. We have all seen hundreds of thousands of faces throughout our lives, so we have an endless supply of characters for our brain to utilize during our dreams." -112.213.219.56 (talk) 17:59, 1 February 2011 (UTC)[reply]

I can't confirm or refute, but I think the claim is untestable. Even careful experiments like the one mentioned here [5] wouldn't be able to determine whether a face was known to a dreamer prior to dreaming. SemanticMantis (talk) 18:20, 1 February 2011 (UTC)[reply]

Sounds unlikely to me. Why is it that we can imagine unique faces for fictional characters in the books we read or write but our brains wouldn't be able to generate new fictional faces while dreaming? Abyssal (talk) 18:22, 1 February 2011 (UTC)[reply]

You get faces in your dreams? For me I either "know" who the person is (by name), or I just get a general idea of them (gender, age) basically an archetype, but no distinct or recognizable face. Ariel. (talk) 19:43, 1 February 2011 (UTC)[reply]

It's nonsense, or at best an unverified theory. 82.43.92.41 (talk) 20:59, 1 February 2011 (UTC)[reply]

Fact: You should be wary of things labeled as facts that don't have supporting citations. --Mr.98 (talk) 21:25, 1 February 2011 (UTC)[reply]

Your wish is my command! ⇈^{[citation needed]}⇈ Nil Einne (talk) 23:52, 1 February 2011 (UTC)[reply]

Sounds unlikely. The mind is perfectly capable of creating new and novel ideas both awake and in sleep, so I don't see why it couldn't create new faces and even modified existing faces. ~A H 1^(TCU) 21:50, 2 February 2011 (UTC)[reply]

A few months ago I dreamed I was (among other characters) a little girl in the far future, and I had three pets, red blue and yellow, which looked like 3-D 3-letter acronyms about two feet long, but I could call out to them "molybdenum, aluminum, uranium" and they would uncoil into colorful taffy-ish pets faintly reminiscent of dogs or cats, and assist me in my adventure to track down Silvio Berlescui's secret wormhole to a limitless supply of gemstones, including such things as sneaking around on a space-yacht with artificial gravity on both sides of the main deck. I mean, there are elements of the dream which are preposterously unfamiliar, and others that were preposterously familiar. When there are so many aliens in my dreams, why should all the human faces be genuine? Wnt (talk) 07:20, 3 February 2011 (UTC)[reply]

water

where can i get a jug that has a valve like this http://www.youtube.com/watch?v=LimbOdetYeM — Preceding unsigned comment added by Tommy35750 (talk • contribs) 19:45, 1 February 2011 (UTC)[reply]

Here are some links: http://www.shopwiki.com/Spigot+Jug Search for "water jug spout" and "water jug spigot" (without the quotes). Ariel. (talk) 19:48, 1 February 2011 (UTC)[reply]

the jug in the vid is a water cooler jug it is pre-filled with water where can i buy this — Preceding unsigned comment added by Tommy35750 (talk • contribs) 21:24, 1 February 2011 (UTC)[reply]

Forgetting the fact that you pretty much make it impossible for someone to help you, even if they wanted to, by not even bothering to mention where on the planet you are; the wikipedia science reference desk is really not the best place to ask for advice on where to do your shopping. Vespine (talk) 23:59, 1 February 2011 (UTC)[reply]

While agreeding with the sentiments, from memory the OP is from New York Nil Einne (talk) 03:39, 2 February 2011 (UTC)[reply]

Most bottled water companies offer it in those big bottles. Just go to their websites. You can usually set up a regular delivery if you drink enough of it. (Of course, most bottled water companies are just bottling tap water, so you really just need the bottle.) APL (talk) 00:53, 2 February 2011 (UTC

it dosent have that valve in it thou. i need it to have the valve

See this, for example. Most springwater companies will stock something like that. But I agree with above, you really just need the bottle. If you really are keen on having pure water, getting a home purifier is cheaper and probably better than buying springwater. Someguy1221 (talk) 06:09, 2 February 2011 (UTC)[reply]

Unknown bullet case

I don't know if this is the right place to ask, but anyway I have a bullet case that has exactly the same measurements of the 8x57mm IS (rim, base, neck diameter, caliber etc.) if not for the length, that is precisely 56 mm, instead of 57 mm, do you think it's the same cartridge case? Other thing, I have a case that is very probably from the Askoriya AMR (same length, colour and shape), but I can't tell, because it has been made into a screwdriver (not my fault). Considering that it is quite dinged up, would it be useful to have a photo of it on Commons or is it superfluous? Thanks, --Amendola90 (talk) 19:53, 1 February 2011 (UTC)[reply]

Why can neurons only use glucose as an energy source?

Like the title states. Why can neurons only use glucose as an energy source? —Preceding unsigned comment added by 137.224.252.10 (talk) 20:34, 1 February 2011 (UTC)[reply]

As I understand it, the restriction to Glucose applies to all forms of cellular respiration in all cell types - not only in neurons. Other forms of energy extraction from more complex molecules, like protein metabolism, fat metabolism, and complex carbohydrate metabolism, occur outside the cytoplasm, as part of the process of macroscopic digestion and metabolism (occurring in humans using acids, enzymes, proteins, and other bio-chemicals made in the pancreas, intestine, stomach, and so on). Nimur (talk) 21:05, 1 February 2011 (UTC)[reply]

Fatty acid metabolism disagrees with you: The enzymes used in fatty acid oxidation in animal cells are located in the mitochondrial matrix. However, Free fatty acid chains of more than 12 carbons require the help of membrane transporters to cross into the membrane into the mitochondria; I presume that neurons just don't express those transporter proteins. –Henning Makholm (talk) 21:45, 1 February 2011 (UTC)[reply]

Nimur, I think you are referring to digestion, which is just the beginning of the process. The cellular metabolism of proteins, fat, and carbohydrates does occur within the cytoplasm, with many of those pathways utilizing the mitochondria and other organelles. This is the basis of biochemistry and cell biology. --- Medical geneticist (talk) 03:35, 2 February 2011 (UTC)[reply]

My error, sorry. I was not aware that those other biochemicals were metabolized inside any cells. So are neurons unique in this respect, in that they lack the metabolism capabilities of other human cells? Nimur (talk) 19:24, 3 February 2011 (UTC)[reply]

One reason why neurons do not like to burn proteins might be that the breakdown of amino acids uses glutamate as a nitrogen sink. Glutamate also happens to be an important neurotransmitter. If neurons were to start producing lots of metabolic glutamate depending on the available nutrients, it would be a problem to get rid of it without disrupting their signaling functions. Simply releasing it into the cerebrospinal fluid to find its way towards the liver is not going to be a good idea.. –Henning Makholm (talk) 22:22, 1 February 2011 (UTC)[reply]

Neurons use glucose as their primary energy source but under certain conditions they can utilize ketone bodies derived from fatty acid oxidation. --- Medical geneticist (talk) 03:35, 2 February 2011 (UTC)[reply]

Bread-maker diagnosis

Recently my bread-maker has started making "bread" which does not rise much if at all, and the upper part of which is crumbly. What might be the cause of this? I'm not sure if this started after I switched to another brand of bread-flour. Thanks. 92.28.247.121 (talk) 22:14, 1 February 2011 (UTC)[reply]

It could be dead or old yeast, try proofing the yeast (basically add some warm water and sugar and see if it foams). Or it could be a low gluten flour, make sure to use bread flour - not pastry flour (and all purpose flour is not so great either). (If you are not in the US those flour terms may not be familiar to you, hopefully someone will translate.) Ariel. (talk) 00:43, 2 February 2011 (UTC)[reply]

Based on my experience, old yeast is the most likely but another possibility is that the bread-maker has a mechanical fault resulting in poor kneading. If the mixing/kneading blade is not turning, the result will be more like pastry than bread (you can get a similar effect by forgetting to put the blade into the machine after cleaning it) - most breadmakers can be opened while they're running so you should be able to check this. You could also try another brand of bread flour. --Colapeninsula (talk) 10:58, 2 February 2011 (UTC)[reply]

I opened a new sachet of dried yeast and put twice the recommended amount in, and now I've got normal bread. I thought it could be because all the ingredients were cold, it being winter. Thanks 2.97.220.121 (talk) 20:08, 2 February 2011 (UTC)[reply]

Depending on how your breadmaker works, that could indeed be the problem. If you're baking by hand, you can start with a tiny amount of yeast even in cold conditions and the bread will eventually rise all the way: you just give it more time. Obviously, the breadmaker isn't able to do that because it is working by the clock, not by the volume of the dough. Solutions are to increase the quantity of starting yeast (as you have done), or pre-warm the flour (and mixing bowl?) in a very low/switched off oven. The first risks making the bread taste more 'yeasty', the second takes a little extra preparation time and an oven. 86.164.58.119 (talk) 21:02, 2 February 2011 (UTC)[reply]

Try adjusting the amount of sugar and salt. More sugar will increase the leavening of the bread while too much salt will impede the yeast action. ~A H 1^(TCU) 21:48, 2 February 2011 (UTC)[reply]