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November 15

physiology

I used to use a program called body works 4.0 to learn about human body, anatomy, etc.

I see this software, even the newest version, is outdated. Does anyone have any recommendations for an easily accessible program geared towards physiology / anatomy?

Outdated how ? Does it show the "proper places to do bleedings" ? :-) StuRat 02:42, 15 November 2006 (UTC)

Bicarbonate vs. Hydrogen Carbonate

I'm doing my science homework and I've been learning about Polyatomic Ions in class and now we're practicing writing formulas and nomenclature. I had to write a formula for Hydrogen Carbonate. I know that there is some controversy weather or not it is the same as Bicarbonate. I thought that the formula for Bicarbonate was HCO₃ and that Hydrogen Carbonate would be H₂CO₃. If anyone knows the answer, this would be very helpful. Thank You -- Jesusfreak 01:51, 15 November 2006 (UTC)

The prefix 'Bi' is sometimes (always?) used to indicate the presence of hydrogen as in sodium bicarbonate (NaHCO₃??)

Ahh! look what I found!

The bicarbonate ion is a polyatomic anion with the empirical formula HCO3− and a molecular mass of 61.02 daltons; it consists of one central carbon atom surrounded by three identical oxygen atoms in a trigonal planar arrangement, with a hydrogen atom attached to one of the oxygens. The bicarbonate ion carries a negative one formal charge and is the conjugate base of carbonic acid, H2CO3; it is the conjugate acid of CO32−, the carbonate ion.

So hydrogen carbonate is bicarbonate!

--Light current 02:12, 15 November 2006 (UTC)

H₂CO₃ is carbonic acid, and it is unstable with respect to loss of carbon dioxide: CO₂ + H₂O ⇌ H₂CO₃. The equilibrium lies heavily away from carbonic acid. Xcomradex 02:29, 15 November 2006 (UTC)

Is that why my lager is fizzy?--Light current 02:31, 15 November 2006 (UTC)

Yes, bicarbonate and hydrogen carbonate are synonymous (HCO₃⁻). In fact, I believe hydrogen carbonate is the IUPAC recommended term (so, for instance, sodium hydrogen carbonate instead of sodium bicarbonate), which is logical: using bi- to indicate the hydrogen is not intuitive. It’s more awkward, though, and in practice the bicarbonate terminology seems to be well-entrenched. — Knowledge Seeker দ 03:31, 15 November 2006 (UTC)

Um, this may be out-of-date terminology for all I know, but I think "hydrogen carbonate" is H2CO3. "Carbonic acid" is hydrogen carbonate dissolved in water. The pure substance, with no water to make it dissociate, is not particularly an acid. --Trovatore 03:40, 15 November 2006 (UTC)

The orinal question was about ions, not full compounds. You're correct that H₂CO₃ would be "hydrogen carbonate", but it would not be "a hydrogen carbonate ion". DMacks 03:47, 15 November 2006 (UTC)

Well just to quote from our page again,

The bicarbonate ion is a polyatomic anion with the empirical formula HCO3

carbonic acid,(is) H2CO3

Seems pretty clear to me! And Im no chemist!--Light current 03:57, 15 November 2006 (UTC)

But it doesn't mention hydrogen carbonate. Our hydrogen carbonate was a redirect to bicarbonate; this seems to have been the clamorous error of some idiot user who calls himself Trovatore. What was he thinking? I guess we'll never know. Anyway, I've redirected it to carbonic acid; I think this is more correct, though technically speaking the pure substance H2CO3 (which, I think, can't exist at standard temperature and pressure, but can exist under other conditions) should be called hydrogen carbonate rather than carbonic acid. --Trovatore 04:34, 15 November 2006 (UTC)

i think it should point to bicarbonate, since someone is far more likely to be wondering about sodium hydrogen carbonate etc than something else. my two cents. Xcomradex 05:15, 15 November 2006 (UTC)

Not a good excuse for inaccuracy, in my view. But if you like, you could make a disambig page. --Trovatore 05:23, 15 November 2006 (UTC)

sounds too much like hard work ;-) --Xcomradex 07:04, 15 November 2006 (UTC)

Meh, who cares where it points, as long as it's clear from that page which one that page is talking about. And provides a route to "the other one". I just added a dablink for that last bit. DMacks 20:39, 15 November 2006 (UTC)

I restored the redirect target to bicarbonate. I have never seen hydrogen carbonate refer to carbonic acid, though if someone has a good source I would like to see it. There is plenty of documentation that hydrogen carbonate refers to the same ion as bicarbonate. See, for instance, this answers.com search (in particular, the Columbia University Press encyclopedia), another search, our own nomenclature articles (see point five), and a PubChem search (and the PubChem listing. — Knowledge Seeker দ 22:07, 15 November 2006 (UTC)

Well what do you think the formula is for carbonic acid?--Light current 00:39, 18 November 2006 (UTC)

I think the formula is H₂CO₃, which should be apparent if you read the article to which you linked. — Knowledge Seeker দ 03:53, 18 November 2006 (UTC)

Exoskeletons

I'd like to bone up on exoskeletons...why exactly can't they grow, leading animals to shed the old before growing a new one ? Mammal bones can grow, including the skull, which is pretty much a portion of exoskeleton. Is there some inherent reason why other animals with full exoskeletons can't do this, or have they just failed to evolve that ability ? StuRat 02:32, 15 November 2006 (UTC)

"This structure makes cuticle extremely strong, as well as highly effective at keeping the spider from drying out, but the material does have one serious drawback. While it's flexible enough for movement, it can't expand like human bones and tissue -- in other words, it can't grow. In order to increase its size, the spider has to form a new, larger cuticle exoskeleton and shed its old one (this is called molting)." Got it from http://science.howstuffworks.com/spider1.htm Hope that helps! (too lazy to sign in) User:Sifaka 152.3.72.50 03:15, 15 November 2006 (UTC)

Thanks, but that only says THAT it doesn't grow, not WHY. StuRat 04:41, 15 November 2006 (UTC)

If you look at this site http://www.cals.ncsu.edu/course/ent425/tutorial/integ.html it has a nice diagram of the exoskeleton cellular layers. The outermost and exposed layers that form the hard inflexible parts of the exoskeleton called sclerites are formed from individual protein molecules that are linked together by quinone compounds. This is a pretty exothermic reaction so these are very stable bonds that are forming and are energetically difficult to reverse. However that isn't enough to explain it. First of all since the sclerites are not composed of living cells and they are on the outside of the insect exposed to air, modifying them, which would take place in an aqueous environment by appropriate enzymes would be difficult. If the insect were to dissolve portions of the whole cuticle at once, it will lose water quickly and open itself to disease vectors. One could imagine an insect sloughing off pieces of its exoskeleton at a time. Human skin which has a similar pattern of layering, but is different in that dead cells take the place of the cuticle. These cells are sloughed off rather quickly and allow a human to grow. An insects exoskeleton can't slough off in tiny pieces like human skin because it is one big interconnected mass. Instead it has to get rid of the whole thing and harden a whole new layer that is big enough for it. That is why newly shed insects are very soft to the touch. Their cuticle hasn't hardened yet. Procuticle has some more information with lots of jargon. Ecdysis, the scientific term, describes the cellular actions behind molting. That is about the best I can do without consulting an entomologist. Sifaka ^talk 05:04, 15 November 2006 (UTC)

Random guess time! Your skeleton is inside you, therefore your bones can grow by adding layers on. For an exoskeleton to grow, the dry outer layer which is not in contact with the useful fleshy parts of the animal would have to have another layer laid down. This is rather hard to arrange. It's possible that I'm in fact saying what Sifaka is saying ("...they are on the outside of the insect exposed to air..."). Skittle 21:15, 15 November 2006 (UTC)

Endoskeletons are remodeled by osteoclasts and osteoblasts continuously breaking down and reforming bone, on both (all) surfaces. These are active beneath the periosteum, the thin membrane covering bones. It is difficult for me to imagine how such an environment could be maintained on the exterior surface of an animal. — Knowledge Seeker দ 22:26, 15 November 2006 (UTC)

I can picture a series of overlapping plates, like roofing tiles, which grow at one end, like fingernails. When needed, a new plate could also grow between two existing plates, to fill in a gap. The advantage of being able to avoid shedding, and the vulnerability that entails, would seem to make this method preferable. So why doesn't it happen ? StuRat 01:10, 16 November 2006 (UTC)

You mean kind of like (fish) scales? I have a feeling it's probably related to the complexity of the organism, since there really aren't any animals larger than insects (which, admittedly, can get pretty darn big) that have exoskeletons. With such a relatively tiny volume, the exoskeleton is competitive with an endoskeleton, whereas larger animals require an endoskeleton. I'm not a biologist, so I can't really say why, though. Virog^{It's not}_{my fault!} 04:08, 16 November 2006 (UTC)

Don't snakes have exoskeletons ? And aren't some of them huge, like an anaconda ? StuRat 07:11, 16 November 2006 (UTC)

No, snakes are vertebrates, which among other things, means they have a spinal column and therefore an endoskeleton. — Knowledge Seeker দ 07:15, 16 November 2006 (UTC) See [1] for a photograph of a snake skeleton, or a Google Images search for more. — Knowledge Seeker দ 07:18, 16 November 2006 (UTC)

It's probably the difference between monocoque and truss structures. 16:39, 16 November 2006 (UTC)

Non-Standard Sleeping Pattern Name

Is there a name for the patter of sleeping 12 hours, staying active for 24 hours, sleeping for 12, and so forth? If so... what is it? Thanks in advance ^^ kaiti-sicle 02:43, 15 November 2006 (UTC)

Well, 12 on/12 off isn't a normal diurnal variation or circadian rhythm, but at least the terms may point you to an answer. Marine life has a 12 hour tidal rhythm, but people shouldn't :). - Nunh-huh 05:52, 15 November 2006 (UTC)

I don't think enough people could follow that schedule that there is a name for it. Many biological rhythms are close to 24 hours. Even when external cues are removed, the drift of rhythm is smaller that that. The system you describe would shift sleep alternately between day and night. In the 1970s, some medical or surgical residencies required every-other-night call, which was essentially 36 hours awake, followed by 8-10 asleep, for 1-3 years with occasional breaks. It was grueling. Currently, residency rules mandate going home after being at work for 24 hours, and people may then sleep for 12 hours, but do not then stay awake another 24 hours-- it is a stressful, unnatural rhythm that cannot be sustained. alteripse 11:45, 15 November 2006 (UTC)

Just a slight nitpick: current residency rules mandate going home after 30 hours, it's just that no new patients can be started in the last 6 hours.Tuckerekcut 15:29, 15 November 2006 (UTC)

I would think that every time an exhausted resident makes a mistake that kills somebody, the hospital would be sued for millions, and this idiotic practice would end. Why doesn't this happen ? StuRat 18:32, 15 November 2006 (UTC)

The issue is complex. For one, rarely can clear-cut situations like that be determined. Also, there are several barriers to reduce the number of resident work-hours. For instance, suddenly curtailing work hours leaves hospitals and programs short of workers; there will not be enough doctors to handle the work (in fact, even the recent restrictions have led to some busier hospital services, which can also lead to mistakes). Another is that with duty hour restrictions, residents will not gain enough experience. Given the choice between longer hours or an extra year of residency, many residents would choose the former. And finally, many doctors believe that physicians have to be “tough” to deal with the stresses they will face and they should get used to a grueling lifestyle. Of course, there are many reasons to limit hours as well—I am not expressing an opinion here. — Knowledge Seeker দ 22:32, 15 November 2006 (UTC)

Two minor additions. The current restrictions did result from a lawsuit over an avoidable death in NYC about 15 years ago. The other significant safety drawback of shorter shifts not mentioned by knowledgeseeker is that reduced continuity incurs an increased patient risk: it will take longer for the new resident to recognize changing status of an acutely ill patient, each sign-out involves a synopsis of the clinical information, and there is often a difference in the level of mental energy exerted on patients signed out to you who have already had their initial plans and evaluation formulated by the last shift. These are very real safety trade-offs to balance against optimized alertness. The typical replacements for residents when work hours are shortened but the patient load must be handled are nurse practitioners who cost more and work shorter shifts. alteripse 23:06, 15 November 2006 (UTC)

The second argument is reasonable, although I picture somebody working for 30 hours straight to be a much higher risk than a new doctor. The first argument, that hospitals won't have enough doctors, is not sound. They will merely need to hire more (and possibly pay more), if the hours of each are kept down. I'm not aware of any absolute shortage of doctors, at least in the US, so it's just an issue of the hospitals being unwilling to pay them adequately for their time. Of course, any change would need to be phased in, to allow for hiring new doctors, but that's not an argument to refuse to make the change at all. StuRat 01:01, 16 November 2006 (UTC)

Hospital practices continue to evolve in attempts to improve patient safety. My points above were not intended to justify "no change", but to illustrate the multiple dimensions of what might initially seem a simple problem. I mentioned nurse practitioners as substitutes for house staff, but the other solution, as you suggested, is much more expensive doctors who have already completed their residencies-- called hospitalists, which can cost as much as 5x what a residents costs. And of course the cost of hospital care takes another upward jump... alteripse 01:13, 16 November 2006 (UTC)

Its actually called Wikipedia addiction 8-)--Light current 20:04, 15 November 2006 (UTC)

Thanks for the info. I was curious because I have a tendency to fall back on that pattern; not consistently but for weeks at a time. kaiti-sicle 02:55, 16 November 2006 (UTC)

Acids

Why do all acids contain hydrogen?--Light current 04:01, 15 November 2006 (UTC)

They don't, although many of them do. The definition of a Lewis acid is a compound that likes to collect a pair of electrons. A better known non-hydrogen containing one is Aluminum trichloride. Electrophiles are by definition Lewis acids.

"Lewis Acids All species have a vacant orbital and/or an available LUMO (Lowest unoccupied molecular orbital)
 and all species with full or partial positive charge behave as Lewis Acids.
 Lewis Acid behaviour is found amongst:

    • Metal cations
    • Electrophiles (attacking Lewis acids)
    • Electrofuges (Lewis Acid leaving groups
    • Lewis acid "ligands" around and anionic centre (H+ and R+)
    • Classic electron deficient species such as boron trifluoride, BF3
    • Cationic spectator counter ions
    • Electron deficient pi-systems which take part in multicentre interactions
" 

Stolen from http://www.meta-synthesis.com/webbook/12_lab/lab.html

Some of the above are kind of complicated if you haven't taken organic chemistry yet. The short answer is many acids have hydrogen because the corresponding thing the hydrogen is attached to is perfectly happy replacing the hydrogen bond which it has to share with the hydrogen with a pair of electrons that it gets to keep for itself.

152.3.72.50 04:07, 15 November 2006 (UTC)

P4reformatted the block quote above. --ColinFine 04:44, 15 November 2006 (UTC)

One reason that many acids (for some definition of "acid" that is more restrictive than the Lewis definition) contain active hydrogen is because that essentially is the standard more-restrictive definition. See Acid#Definitions of acids and bases for more definition info. It began as a descriptor of materials that had a common property...only later was is ascribed to "has active hydrogen". DMacks 06:04, 15 November 2006 (UTC)

High specific heat of water relating to exothermic reaction (simpler question on paragraph 3)

Because water has a high specific heat will an exothermic reaction such as, heat escaping to the atmosphere after heating or more specifically to a calorimeter, progress slowly compared to the progression of the endothermic reaction taken place during the actual heating. If yes would a measurment of heat capacity be calculated wrong if temperature is measured before exothermic reaction is complete? or would it not matter when you measure the water during the exothermic reaction. 69.150.209.13 05:31, 15 November 2006 (UTC)

Um, what reactions are you talking about? Transfer of heat, by itself, isn't a chemical reaction at all; it's neither exothermic nor endothermic. If you're trying to measure the heat capacity of water by adding a known amount of heat energy and then measuring the temperature, you should do so immediately. If you wait until all the heat escapes and the water is back to its original temperature, you'll get a heat capacity of infinity, which is obviously wrong. —Keenan Pepper 06:41, 15 November 2006 (UTC)

During a chemistry lab, we were told to get the heat capacity of a calorimeter. By heating one beaker of 50mL of water and leaving another 50mL in a styrophome cup. Then to measure both temperature: cool (22 C) hot (42 C) - my results. Then we were told to mix the water. the temperature of the new warm water was 35 C. The hot water seemed to lost only 7 degrees. amd the cool seemed to gain whole 13 degrees. Ideally it was said the heat transfer is supposed to be moderatly equal. I do not understand why I got these reuslts. I apologize for my errors in the first question. I wanted to make it simpler but made it more complex 69.150.209.13 08:24, 15 November 2006 (UTC)

That doesn't sound that far off. Did you use a fancy digital thermometer or a regular liquid thermometer? Probably the 22 and 42 measurements happened to be a little low and the 35 to be a little high. —Keenan Pepper 15:56, 15 November 2006 (UTC)

Was the transfer done such that the cold water was added to the warm water in the beaker? If that's the case, it could be that the beaker was warmer than the water, and was still transferring heat to the water when the cold water was added.--Mabris 16:46, 15 November 2006 (UTC)

The beaker wouldn't have to be warmer. Assuming the beaker was 42°C as well, the system would a temperature that can be concluded from making the calculations on 32°C water, 42°C water and a 42°C beaker. 35°C seems very plausible in that scenario. TERdON 02:40, 18 November 2006 (UTC)

Hydrocarbon fuel cells with proton-conducting electrolytes

This question is about fuel cells that run on hydrocarbon fuel rather than H₂. If the electrolyte conducts O²⁻ ions, I can write down the half-reactions and everything makes sense, but if the electrolyte conducts protons, I'm not sure what goes on. Is CO₂ formed at the anode? If so, it seems like some electrons are wasted, because carbon is oxidized and oxygen is reduced at the same place, and the electrons from that redox couple don't flow through the circuit. Is that accurate? —Keenan Pepper 05:53, 15 November 2006 (UTC)

The applicable half-reactions are in the article Direct-methanol fuel cell. The electrolyte conducts protons, C is oxidized at the anode (producing CO₂ as you had guessed) but the reduction of the oxygen occurs at the cathode. --Mabris 17:06, 15 November 2006 (UTC)

Oh, I see where I went wrong. I had the hydrocarbon reacting with O₂ at the anode, but really it reacts with water and makes more protons and electrons, so the total number of electrons is the same no matter the electrolyte. Thanks! —Keenan Pepper 21:09, 15 November 2006 (UTC)

redox potential

Generally NAD is said to be having more negative redox potential than FAD.......and also NAD is capable of donating electrons to FAD but not in a reverse manner ie from FAD to NAD in normal conditions...My question is in what conditions FAD can donate elecctrons to NAD?{i know one example of this kind that is formation of acteyl Coa from pyruvate.here FAD accepts electrons and donates them to NAD...enzyme acting here is pyruvate dehudrogenase complex. how is this possible?)--hima 09:19, 15 November 2006 (UTC)

Since FAD is covalently bound to a protein the amino acid side chains can signifiantly change the chemical environment. This context is the critical factor. David D. (Talk) 12:20, 15 November 2006 (UTC)

The energy to overcome this reaction which seems to work against the redox potentials comes from the oxidization of the Coenzyme A to acetyl-CoA and CO₂. The pyruvate dehydrogenase coordinates the reaction to make this thermodynamically feasible.--Mabris 16:53, 15 November 2006 (UTC)

thx for ur answers....there is even one more issue in this case..that is FAD here is first of all a co-factor for the enzyme....and so as a co-factor it accepts electrons inorder to regenerate lipomide..an enzyme in this multienzyme complex..and transfers them to NAD inorder to release more amount of energy...--203.109.89.230 09:31, 16 November 2006 (UTC)

Watts in terms of volts - equation please

What's the equation linking Watts and volts? I have a feeling it's W=IV^2 or something like that. Thanks, --86.146.247.51 12:10, 15 November 2006 (UTC)

P = IV —Preceding unsigned comment added by 138.29.51.251 (talk • contribs)

Power (in watts) = Voltage (in volts) x Current (in amps), i.e., P = VI. You can substitute in Ohms Law (V = IR) to get other variations on this. (edit conflict)--jjron 12:17, 15 November 2006 (UTC)

See electric power. Gandalf61 12:20, 15 November 2006 (UTC)

Thanks everyone.86.146.247.51 12:22, 15 November 2006 (UTC)

Power=Current times voltage =Current squared times resistance=Voltage squared divided by resistance assuming direct current or alternating current with unity power factor (resistive load). If the circuit contains inductance or capacitance, then consult power factor. Edison 15:32, 15 November 2006 (UTC)

I know I'm being an annoying pedant, but can we be physicists and say potential difference, not voltage!? Englishnerd 22:25, 15 November 2006 (UTC)

Alessandro Volta would be weeping in his grave hearing you say that. Vespine 23:24, 15 November 2006 (UTC)

I dont know, can you? But if you want to be pedantic you should say electrical potential difference to distinguish from other sorts of potential.--Light current 04:35, 16 November 2006 (UTC)

Ah, Touché! Englishnerd 18:40, 16 November 2006 (UTC)

Sam Ting. Edison 05:36, 16 November 2006 (UTC)

Who was Sam Ting and what did he discover in the field of electricity? (I'm joking! :P 192.168.1.1 6:55pm, 16 November 2006 (PST)

Magnetism

I recently had a question on a test for MRI. The question was "What is not a characteristic of a magnet? The answers where a. attracts, b. holds iron, c. dipoles, d. resistive. I need to know if a characteristic of a magnet is that it holds iron? I was confused because I answered resistive. But after looking up resistive in the dictionary (which is a term used normally when talking about electronics) I found that resistive can also mean repel..I think the question was worded badly. Can anyone share some insight?

I'd say the most probable answer is d. All the others are certainly characteristic of a magnet, but only d is questionable. And when the word resistive is used in science, it can safely be assumed (at least I would) to refer to electrical resistance, which isn't characteristic of a magnet. –Mysid☎ 14:07, 15 November 2006 (UTC)

Superconducting magnets are often used for NMR, right? It's definitely D. —Keenan Pepper 15:39, 15 November 2006 (UTC)

• Surely there are non-ferrous magnets around... I'm having doubts about B. - Mgm|^(talk) 09:26, 16 November 2006 (UTC)

When we studied physics, we knew only about ferrous magnets. Assuming that the text book is yet to be updated, d would be the most suitable answer.--Wikicheng 13:04, 16 November 2006 (UTC)

Is 'none of the above' a suitable answer? Most contemporary MRI machines are electromagnets, meaning that they utilize magnetic fields produced by electricity circling through coiled wires. If the wires are electrically resistive, this means that you have to continuously pump more electricity into the wires (coils) to sustain the magnetic field. This is a 'resistive' electromagnet. Most, but not all, contemporary electromagnetic MRI machines are superconducting, meaning that the wire used for the coils has an electrical resistance that approaches zero when the wire is at certain temperatures. These are akin to perpetual-motion machines in that once the electricity is in the coil, you can disconnect if from the power source and the electricity will just keep circling, indefinitely, as long as the wire remains superconducting. Tgilk (talk) 14:18, 12 September 2009 (UTC)

low tech derusting and plating

I've heard there was a way to clean and plate iron such as found in old hammer heads by leaving them in molasses and then putting them in some kind of electrolyte with copper pennies. How this work and what would the setup be? 71.100.6.152 17:13, 15 November 2006 (UTC)

I'd use quick-hard instead of the molases, and you can electroplate things at home with reasonable materials - sulfuric acid (WEAR KITCHEN RUBBER GLOVES BE NEAR RUNNING WATER HAVE A SAFETY MASK OR GOGGLES), copper, distilled water, CuSO4, wires and a battery. More info for home electro-platers findable at [2]. READ THE SAFETY NOTES BEFORE ATTEMPTING ANYTHING AND HAVE COMPOTENT PROFESSIONAL SUPERVISION. JBKramer 17:43, 15 November 2006 (UTC)

Would that [be] quick-hard lime? [(To replace the molasses?)] 71.100.6.152 18:36, 15 November 2006 (UTC)

No, it works only on metal. It is a hardening agent. JBKramer 19:19, 15 November 2006 (UTC)

In our area the stores no longer carry battery acid of any other form of sulphuric acid and the one feed store that carries copper sulphate charges way too much. Is there a process whereby we can use other materials instead? 71.100.6.152 01:28, 16 November 2006 (UTC)

See also Phosphoric acid#Rust removal (aka "Naval Jelly"). In a pinch, maybe Coca Cola or Pepsi Cola would do, given enough time as they both contain some small amount of phosphoric acid.

Atlant 17:51, 16 November 2006 (UTC)

Okay. Found some battery acid today and some copper sulfate at about $4 per lb of acid and $8 per lb of sulphate. This should be enough to do the hammer heads although I like what I have now read about using phosphoric acid and then oil or paint. All I need to know is how to setup the electrolyte bath and the right voltage and current to use. I don't want to turn this into a hobby but just to get an idea of how its done and do a few parts to be sure I know what I'm doing. 71.100.6.152 00:51, 17 November 2006 (UTC)

nuts and bolts

I have a 'guiness book of records' type question - is this ok?

What is the largest nut? On a swing bridge I have observed hex nuts appox 2ft diameter, 1ft depth and approx 1ft bolt diameter - does anyone know of much larger nut and bolt combinations. Thank you.

If you're looking for the biggest nutter, you may well have come to the right place. :) DirkvdM 09:13, 16 November 2006 (UTC)

This nut/bolt combo looks roughly the same size as yours, and it used to build the Grand Coulee Dam. Laïka 15:28, 16 November 2006 (UTC)

Thanks, but the nuts I mentioned are at least twice the size of those (and therfore 8 times the weight) - I doubt anyone, even a professional weightlifter could carry one. Unfortunately I don't have a picture of one - anyone else got anything?

Its not the nut thats the problem, its the size and weight of the spanner (wrench) to turn it. This I think may be the limiting factor--Light current 16:04, 16 November 2006 (UTC)

Interesting - in the case of the bridge I mentioned the nuts/bolts shouldn't be under extreme load since they merely affix the bridge deck to the bit that rotates underneath - so they probably aren't that tight. This leads to the 'worlds biggest spanner' question...

how to test out reactolite (photochromic) spectacle lenses?

i just bought a pair of prescription specs with reactolite lenses - but after 8 hours of use i haven't noticed them go dark! this included walking around outside in a cloudy uk november day for several hours, and staring up at my kitchen fluorescent lamp for a few minutes. neither of them had any noticeable darkening affect!

how can i test if they are working and be sure they're ok once and for all? obviously its a bit difficult finding bright sunshine in the uk in november.86.31.114.97 20:12, 15 November 2006 (UTC)

A flashlight might do the trick. I suspect there is not too much difference in luminescence between a cloudy day and a fluorescent lamp. --HappyCamper 20:14, 15 November 2006 (UTC)

These types of glasses only change color when exposed to certain frequencies of light. I suspect that light filtered through clouds is just not bright enough and light from a bulb or fluorescent lamp doesn't contain the right frequencies (ie why would you want your glass to go dark inside a building?). You could try a full spectrum bulb or just wait for a sunny day to test them. --Cody.Pope 21:14, 15 November 2006 (UTC)

You need real UV light, since I have a pair. Usually the stores that sell them have a little display that has UV light. Failing that, the local donut shop has a counterfeit money detector... --Zeizmic 21:21, 15 November 2006 (UTC)

Also, I just found a website that says the lenses need a 'break-in' period, before they will work as desired. --Cody.Pope 21:23, 15 November 2006 (UTC)

Also that means you have to buy donuts! 8-)--Light current 16:12, 16 November 2006 (UTC)

What if you don't have a gallbladder?

About a year ago, I had my gallbladder removed because of gallstones. The gallbladder is one of those body parts that you can live without just fine, but I'm curious about how the body changes to accomodate the lack of one. I haven't found any answers to that, either online or in the articles on gallbladder, liver, and bile. Basically, the gallbladder stores bile from the liver and then releases it into the small intestine when it is needed. Where does the bile go if you don't have a gallbladder? Does it get stored in the liver, or does it get released directly into the small intestine? —Cswrye 21:25, 15 November 2006 (UTC)

I think you should ask the surgeon who removed it what they did with the connecting pipes - that should give you the answer..

I thought the gall bladder made bile -which we dont need.--Light current 22:08, 15 November 2006 (UTC)

The gallbladder is connected to the main bile duct, which also connects the liver to the small intestine. In a normal person, most bile gets diverted into the gallbladder, but bile can also pass directly through the duct into the small intestine. Without a gallbladder, the only place that bile can go is into the small intestine, but I don't know if the liver compensates for the lack of a gallbladder by storing bile in its place instead of releasing it into the bile duct. If so, I wonder if that puts any extra strain on the liver. If it doesn't, I wonder what the intestine does with all that extra bile. —Cswrye 22:32, 15 November 2006 (UTC)

After the gall bladder is removed, the liver still makes bile and secretes it into the small intestine via the common duct. Bile emulsifies fats so that dietary fats can be digested by enzymes and transported into the blood or lymph system. Gallstones are usually made of cholesterol, which is a component of bile. [3] I'm assuming that liver stores the bile, I mean, it stores so many other things as well. Chickenflicker 23:04, 15 November 2006 (UTC)

Aha! I found this article: Bile canaliculus. A Bile canaliculus is a "thin tube that collects bile secreted by hepatocytes", hepatocytes being liver cells. They "merge and form bile ductules, which eventually become [the] common hepatic duct Note that they are also called biliary canaliculi, which are defined as "any of the intercellular channels between liver cells" [4]. Chickenflicker 23:04, 15 November 2006 (UTC)

Humans do not currently have a need to store bile (the only role of the gallbladder). When the gallbladder is removed, you are essentially losing a side branch of an otherwise straight tube. The straight tube (common bile duct) still exists. Bile flows from the liver through the bile duct to the small intestine. The only difference after removal is that it doesn't spend time in the gallbladder before entering the small intestine. Also, the liver does not store bile. InvictaHOG 23:29, 15 November 2006 (UTC)

I disagree. Bile is needed to digest fats, and the gallbladder helps to regulate the release of bile to match the consumption of fats. Without it, you probably aren't as able to digest fat. This could cause diarrhea, if you have a high fat diet. If so, I suggest reducing your fat intake to a level that the small continuos flow of bile can handle. Of course, a low fat diet is also a good recommendation for everyone, at least low animal fats. Fish and vegetable fats may actually be beneficial. StuRat 00:25, 16 November 2006 (UTC)

My mum had hers removed after some complications involving gall stones and even since she has found she has to live on a very low fat diet to avoid feeling ill. Plugwash 00:50, 16 November 2006 (UTC)

Removal of the gallbladder does not destroy the ability to produce bile, just the ability to store it. After a cholecystectomy, one may feel ill after ingesting meals high in fat, but moderately fatty meals should be perfectly fine. It is only when a large amount of bile is needed, more than can be produced and excreted over a short period of time by the liver, that discomfort is likely to occur. It's like if you replaced the hot water heater in your home with a much smaller one. It would be okay to take a quick shower, but things would get uncomfortable if you try to have a long soak. Tuckerekcut 01:28, 16 November 2006 (UTC)

In high school, while dissecting a frog, I poked the gall bladder with a scalpel, and it squirted the full load into my eye. I haven't been normal since. Edison 05:39, 16 November 2006 (UTC)

Thanks everyone! This has actually been very informative. I never could get a satisfying answer from my doctor, who just insisted that it wasn't a big deal. Losing a gallbladder really isn't that bad, but I figured that it had to affect something. —Cswrye 06:29, 16 November 2006 (UTC)

Making magnets

Rently, I purchased a pair of magnets (I think that they were made of neodymyum or something that sounded like that) which were gold plated, from [[5]] and I was wondering, how do they make them if they are so magnetic? If they use machines, which they probably do, are the machines' "hands" or grabbers or whatevers made out of plastic so the magnets don't stick to them? How do they manufacture them without them sticking to the machinery and ruining it? Thanks for your answers. Ilikefood 21:37, 15 November 2006 (UTC)

Per Magnet , permanent magnets are made with the magnetic field from an electromagnet or a solenoid, although stroking a ferromagnetic material with a magnet will magnetize it somewhat, as will vibrating it in the presence of a magnetic field. Some magnets are heated above the curie point before magnetizing. Edison 22:34, 15 November 2006 (UTC)

rare earth magnets (like yours) are manufactured by machining the sintered material before it is magnetic, then gold plating them to seal out the atmosphere. the final step of the process is to magnetise them. an overview[6] --Xcomradex 22:50, 15 November 2006 (UTC)

I just want to say that this is a great question!! I read it 1st and kinda thought it's a pretty silly question, then I double take and go well hang on, you've got a point, how DO they do it?! Something I didn't know that never even occured to me. Thank you:). Vespine 23:12, 15 November 2006 (UTC)

remembering of course, there is a whole bunch of non-magnetic materials that can be used in place of steel. eg. copper, silver, aluminum, lead, magnesium, platinum and tungsten are not magnetic, nor are most ceramics, glasses etc. you can even get non-magnetic steels, eg[7]. Xcomradex 00:15, 16 November 2006 (UTC)

At the NHMFL, they use beryllium copper tools instead of steel ones to avoid accidents. —Keenan Pepper 01:54, 16 November 2006 (UTC)

Thanks. Ilikefood 22:06, 16 November 2006 (UTC)

Cellulose found in paper

What type of cellulose is found in paper? If it is just plain "cellulose", where/how would I find its refractive index? Chickenflicker 22:49, 15 November 2006 (UTC)

Well, the plain cellulose article does say Cellulose is the major constituent of paper, so that's one, as far as refractive index goes? As for refractive index, that's a good one! No idea... having a look at [list of indices of refraction] I'd put it somewhere around glycerol, around 1.4, but that's just a guess, more then water 1.3, less then glass 1.5. Vespine 23:05, 15 November 2006 (UTC)

A google search for "cellulose refractive index" turns up some stuff around 1.5 - however the amount of water absorbed alters the value - lowering it according to one source?

Yeah, I've been trying Google, but all of the "celluloses" that I found seemed to be synthetically made, rather than just cellulose from plants and such. This is actually an extention of my question "why does grease turn paper clear," since I haven't been able to find a clear answer, after asking: http://answers.google.com, the Ref. Desk [8], my chemistry teacher, and an organic chemistry teacher at UMD. --Chickenflicker 01:26, 16 November 2006 (UTC)

Your refractive index line of reasoning is valid. According to the info one can find at The TexLoc Closet (textile related) site, the refractive index of different celluloses varies from 1.47 to 1.54. Water is 1.33. Plasticsusa.com gives the values for celluloses as 1.46 to 1.51. At Refraction Index of Various Substances for 3D modelers (important if you are programming for PovRay or the like) the RI for Glycerin is given as 1.473, and for various oils it is 1.47-1.54. Thus, pure cotton cellulose paper should be quite transparent when oiled, depending on your oil selection, but in the case of commonly used modern papers, the transparency and colour of would be influenced by non-cellulose ingredients, such as rosin, starch or gelatin applied during sizing, fillers (such as CaCO₃, other chalky materials, dyes and pigments), and whitener such as TiO₂ (with a refractive index of 2.4, and an pretty efficient opacifier)). Seejyb 11:26, 16 November 2006 (UTC)

A very helpful response. =) Thanks! Chickenflicker 05:36, 17 November 2006 (UTC)

HOW DO BOATS STAY AFLOAT?

I would like to know how ships stay afloat without sinking?

thank you,

Isa Abdullah

The weight of the water displaced equals the weight of the boat. Or, if it floats your boat, you can think of the air below the waterline not pushing down as hard as the water below the boat is pushing up. See buoyancy. StuRat 00:15, 16 November 2006 (UTC)

I think you mean the weight of the water displaced by the hull of the boat is equal to or in excess of the weight of the boat and what it contains. Hence a boat made of many tons of steel can float in water because it displaces (by occupying space where water would otherwise be) more water than all of that steel, the cargo, the crew, the air, everything that the ship is made of, contains, or has on it. Robovski 04:35, 16 November 2006 (UTC)

I ignored the weight of air, as that's quite insignificant compared to the weight of water. I am including the weight of the cargo, crew, and anything else in the boat, of course. I disagree, however, that the weight of the water displaced can exceed the weight of the boat, et all. If this was the case, the boat would float higher in the water until the weights were equal. StuRat 07:01, 16 November 2006 (UTC)

I've always found the above standard answers don't quite clarify it very well for people who don't get it. 'Displacement' refers not really to water being moved or something (although in a sense it is) but to the volume of the boat below the waterline. The amount of water that would have been there has to be heavier than the boat itself (plus the air, cargo and crew and what have you). The material of the boat itself may be heavier than water (per volume!), but it forms only the outer layer. Inside it is air, which is negligible in weight. But it does add to the volume. The central term here is density, which is mass ('weight') per volume. The thing to keep in mind is that you have to divide the mass of the boat (plus contents) as a whole by the volume below the waterline. If the boat floats than that is equal to the density of water (1 kg/l). You could say that to the water it is as if there is water there because the average density is the same. If you add weight to the boat, the volume below the waterline will have to increase too, to keep the mass/weight balance equal, so the boat sinks a little, so the boat 'sinks' a little to compensate. I hope that made it a little clearer. Please say if there's something you don't get yet, so we can come up with a better answer (and add it to the buoyancy article). DirkvdM 09:38, 16 November 2006 (UTC)

Here is another version. I'll try to explain why anything floats. Hope it doesn't add to the confusion :-). When a body is put in water, it displaces some water. It also loses some weight. (If you measure the weight of a 1 kg stone immersed in water, it would weigh less than 1 kg). The weight it loses is equal to the weight of the water displaced. Suppose you have a steel ball which weighs 1 kg in air. When you immerse it in water, it displaces some water. Suppose that the weight of the water it displaces is 250 g and hence the ball loses 250 g. Now the apparent weight of the ball (the weight when it is in water) would be 750 g. Let us say that you make the ball hollow, but without altering its weight. Now if you put it in water, you'll find that it displaces more water. Let us say 400 g of water is displaced. Now the ball loses 400g and apparent weight of the ball would be 600g. Suppose you increase the size of the hollow such that the weight of the water it displaces is 1 kg. Now when you put it in water, the weight it loses is 1 kg. that would mean that the apparent weight would be zero. This is when the ball starts floating.--Wikicheng 13:26, 16 November 2006 (UTC)

---

Here's a somewhat related gedanken. Say you have a perfect cube submerged in a tank of inviscid fluid that's resting on the bottom of the tank (which is perfectly flat). The density of the cube is less than that of the fluid. Does the cube float? Virog^{It's not}_{my fault!} 08:50, 17 November 2006 (UTC)

Suppose the volume of the cube is V. When it is fully submerged, it will displace the fluid of volume V. You mentioned that the density of the cube is less than that of the fluid. That means that the fluid displaced will weigh more than the cube, which means that the cube has lost more weight. It should experience an upward force equal to the that of the additional weight it has lost. It will raise to the surface and will float. -- Wikicheng 09:48, 17 November 2006 (UTC)

Have you tried looking at the forces on the cube? Merely looking at displacement won't necessarily answer the question: since the cube is resting at the bottom of the tank, there's no fluid pressure on that lower surface, which is necessary for causing buoyancy. It's an unstable equilibrium. Virog^{It's not}_{my fault!} 18:01, 17 November 2006 (UTC)

For another example, one which is perhaps easier to intuit (am I using the word right?), imagine a suction cup stuck at the bottom of a filled bathtub. The suction cup can stay at the bottom even if it is less dense than water overall. --71.244.101.6 18:21, 18 November 2006 (UTC)

November 16

electric bike

I am working on a project to build an electric bike similar to the one being sold by Golden Motors (China)that uses a brushless DC motor/generator inside a front wheel hub. It costs $175 plus about $60 for shipping to where I live but I think I can do a better job for less money and learn alot about motors and generators along the way in addition to having a lot of fun. Any design or construction tips or suggestions about where to buy magnets etc.? 71.100.6.152 01:50, 16 November 2006 (UTC)

That kit is remarkably cheap, in my view. I very much doubt that you'll be able to build something cheaper. Better, perhaps, but not cheaper. Regardless, I'm almost certain you won't be able to build an electric motor that's competitive with factory-built ones. -Robert Merkel 05:01, 16 November 2006 (UTC)

Mother Earth News had plans in the 1970's for electrifying a bicycle with a 12 volt starter motor from a car. The kit price sounds reasonable. Edison 05:42, 16 November 2006 (UTC)

Yes, very reasonable but it won't help me learn anything about building various types of practical DC brushless motors unless I try to take it apart. 71.100.6.152 11:02, 16 November 2006 (UTC)

I liked looking at the products, and we actually have something on this: Brushless DC electric motor, which is a very interesting read. Looks like China has an advantage here, since these motors must be hand-wound, and use custom circuit boards. It would be difficult to do it yourself, but you could take apart hard-drive and fan motors to see how they work. People are doing this for electric model airplanes. --Zeizmic 13:52, 16 November 2006 (UTC)

Yes I've taken a broken fan motor apart to see how it worked and read about modelers using 58x CD drive motors in model airplanes. In fact after one shattered a CD and busted the drive I thought about using it for something like that myself but I wanted something with enough power to get me up a hill on a bike (which is hard sometimes with a ull load of groceries) as well as using it to charge the battery coming down hill as well as break the decent. I don't theink the motor from China is going to have the power I want. All I really need are coils, magnets, Hall effect switch and a battery right? 71.100.6.152 15:46, 16 November 2006 (UTC)

energy

what criteria must be met before energy can be conserved?

First sentence of Conservation of energy? --Wirbelwindヴィルヴェルヴィント (talk) 02:11, 16 November 2006 (UTC)

But maybe you're talking about energy conservation ? StuRat 06:56, 16 November 2006 (UTC)

Conservation laws arise from continuous symmetries. Specifically, energy is conserved if physical laws are invariant with respect to translation in time. See Noether's theorem. Gandalf61 11:54, 16 November 2006 (UTC)

The big rip, explained for a layman?

Recently someone posted a link to the big rip in a discussion about the universe. I have to say I didn't really understand that article, especially this sentence: "...this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point gets ever closer. When the size of the observable universe is smaller than any particular structure, then no interaction between the furthest parts of the structure can occur" If the edge of the universe is moving away (from us?) at the speed of light, how can it "get ever closer" ? As best I understand it, while the physical objects like stars and galaxies are, in fact, moving away from each other in the macroscopic universe; per the Big Rip theory whatever invisible stuff makes up the fabric of the universe is shrinking, and so while that shrinking can't be perceived or measured (?) in the macroscopic universe, at a quantum level it is still affecting the macroscopic universe. Is that correct? What is that "stuff" that is shrinking, anyway, and how does it relate to other theories of matter and existence, like string theory? What would be some other articles to read? 192.168.1.1 6:59pm, 15 November 2006 (PST)

The key term there is "observable" - while the actual universe is getting bigger, the area that we can see is getting smaller. There is no "shrinking" in the classical sense, other than the amount of stuff we can see is shrinking. Another article that was not listed under the See also section would be cosmic inflation, though that might be a bit difficult to read. Virog^{It's not}_{my fault!} 03:08, 16 November 2006 (UTC)

It's good to know we've got about 20 billion years before the end of time. --Cody.Pope 05:12, 16 November 2006 (UTC)

It is confusingly phrased and should probably be corrected. Here is my explanation: If you have climbed a tower, the horizon is far away; then as you go down the horizon gets closer and closer. This movement of the horizon is not a real movement, and the horizon is not real but only a virtual thing. The edge of the observable universe is like a horizon, it is also virtual. To someone who is (with respect to us) at that edge, there is nothing remarkable there. But we are at the edge of her observable universe. This edge is very similar to the event horizon of a black hole. In fact, you might say we are living in the non-black part of a black hole turned inside out (just like haggis is a sheep turned inside out). Everything beyond the edge is black: nothing, not even light, can escape from there to us. While space rushes out, the blackness moves in. The edge is where space rushes out at the speed of light.  --Lambiam^Talk 08:29, 16 November 2006 (UTC)

induction heaters

I was surprised to find that there are three types of induction heaters. One appears to use a coil with high frequency (20khz) alternating current flowing through it to heat a "core" of magnetic material placed inside the coil and the second appears to heat non-magnetic but electrical conductive materical that has been formed into a closed single turn secondary coil around a closed core with a primary coil and the third is magnetic material inserted between the ends of an open core. Can anyone tell me how each of these induction based heaters work, if there any other types of induction heaters and if is there a working circuit diagram for each type of coil anywhere? I've only found a few homemade coils on You Tube and other places but no circuit diagrams or details of how they work. 71.100.6.152 11:33, 16 November 2006 (UTC)

Have you already read our Induction heating article? (I know it's a bit sparse.) What points do you need more info on?

Atlant 18:00, 16 November 2006 (UTC)

Well a complete circuit diagram and parts list would be nice for one homemade unit I've seen at You Tube. 71.100.6.152 23:23, 16 November 2006 (UTC)

PLC

hi,can you please give me some information about different methods of communication in a programmable logic controller with an input device such as computers i am sepecifically after some information with the use of following devices →twisted cable →co-axial →fibre optics please reply me with the use of these devices in PLCs including there advantages and disadvantages olus their use in industry.

Essentially, the various physical layers and communications protocols just provide varying trade-offs between cost, distance, speed, reliability, configurability, and the like. Roughly speaking, ranked in order of increasing cost, you might find:

1. Twisted pair (whether point-to-point or multidrop)
2. Coaxial cable (point-to-point or multidrop)
3. Fiber optics (always point-to-point)

A PLC easily generates twisted-pair, coax, and light-emitting diode-driven-fiber protocols. It'll cost you some serious money to generate long-haul, laser drive fiber protocols.

After reading all that (and the referenced articles), do you have a more-specific question?

Atlant 18:06, 16 November 2006 (UTC)

RPM

How many rpms would a fan blade have to spin at to generate wavelengths of visible light? And is it possible, or would ho-hum-trillion rpms be too much for any physical structure to tolerate?--172.134.127.134 15:47, 16 November 2006 (UTC)

(My area is way lower frequency phenomena, but I will have a go at it. Those skilled at fields and waves please correct any misstatements.) First determine why a spinning fan blade would generate electromagnetic waves at any frequency. Do they have magnets attached?(careful, they will fly off when you least expect it). Or are the blades electrically charged? If it had 2 blades with opposite electric charge on them or opposite magnetic polarity, it would be a rotating dipole. It would generate an alternating field as it rotated. The wavelength is so short that the rotating fan blade could be submicroscopic and still be an efficient radiator. Electromagnetic spectrum says the longest wavelength (lowest frequency) of visible light is 700 nm (red, right next to infrared in wavelength). To get frequency, divide the speed of light by the wavelength: frequency=c/wavelength = (3*10^8 m/s)/(700*10^-9 m)=4.28 *10^14 Hz. Multiply by 60 to get revolutions per minute: 2.57 * 10^16 rpm, or 25,700,000,000,000,000 rpm. It would have to be down at the atomic or molecular level to not fly apart from the radial forces. The article Micropower tells how researchers are actually fabricating tiny high speed turbines and generators out of etched silicon wafers, using technology derived from integrated circuit construction. They have built a generator 10 mm wide which spins at 100,000 rpm, with higher speeds in the works, but this is many orders of magnitude larger and slower than what your fan based optical generator would require. Edison 17:21, 16 November 2006 (UTC)

If f is the frequency and r the length of a blade (the radius of the fan), the tip moves at a speed v = 2πfr. Since v < c, r < c/(2πf). Using f = c/λ (see Edison's reply), this means r < λ/(2π) ≤ 700/6.28 nm = 111 nm. This is truly a nano engine.  --Lambiam^Talk 18:37, 16 November 2006 (UTC)

<joke>The fan will be generating visible light far earlier than that, when its motor catches on fire at such a high RPM. </joke> 22:39, 16 November 2006 (UTC)

Eyeglass prescription

Is the following idea obsessive-compulsive or is it sound? I can't tell.

I have a new prescription for my very first pair of eyeglasses:

		Sphere	Cylinder	Axis
Distance Vision	oculus dexter	+0.25	-0.75	180
	oculus sinister	-0.25	-1.00	010

They say you should renew the prescription every 2 years, and my insurance only pays up to $340 CAD once every 2 years, so basically I will be wearing these for quite a while. So I want to make sure they are 100% physically accurate to my eyeball needs.

As such, I am very tempted to go to a totally different optometrist and actually pay the money for a 2nd prescription, just to compare with the first one and "make sure" it's 100% accurate. Theoretically the two prescriptions would be exactly the same, although something tells me they probably wouldn't be.

Any thoughts or knowledge on this matter? --Sonjaaa 16:05, 16 November 2006 (UTC)

Yes - from personal experience - once your eyesight settles down (mine got worse up to the age of about 16 and hasn't changed much since then - might be something to do with puberty and adult head shape?) the prescription won't change much - on repeated eyesight tests (at the same and different opticians over 5 years)I got roughly the same every time - but it does differ from time to time - by a very small amount - I assumed this was due to experimental error - and the human body is not a rigid thing - so mabye the perfect presciption varies from day to day. More noticably I noticed a very big difference with lenses made to the same prescription from different manufacturers. In the UK the eyetest is cheap but the glasses are expensive so it's not a big problem to get your eyes tested again. —The preceding unsigned comment was added by 87.102.1.174 (talk • contribs) 18:51, November 16, 2006 (UTC).

(insert usual disclaimer about this not being medical advice... if you die because of what I wrote, you can't sue me from the grave, etc etc...)

As someone who has been wearing glasses since the age of six, I can tell you that "accurate prescription" is very loosely defined. Your eyes work better and worse in different circumstances, you'll find that you see worse when you're tired, at the end of a long day, if you've spent a long time in front of a screen, in bad lighting conditions (dusk, especially), etc. So there is no one "true" prescription for you.

Second, the major cost in changing prescriptions is the frame, not the lens (at least, that's been my experience in Europe, although I imagine in holds true in Canada as well). So once you get a frame, you can change the lenses without having to buy a new frame. So even if you feel your first prescription is 'off', you can always try it out for awhile before deciding whether you want to change it. Do make sure to enquire as to the cost of frame+lenses or just lenses at your optician's before going down this road. Note that there are several different kinds of lenses (plastic, glass, coated plastic...), your optician will explain the differences, advantags and disadvantages to you.

With a weak prescription like yours (1 diopter is nothing!), your eyesight is still very good, and the difference that + or - 0.25 or 0.5 in either direction will do is minimal, you will barely notice it. I don't think it's worth getting fussed up about, especially taking into consideration the variability of your eyesight (as mentioned above).

There is the added factor that, for a given eye, there is a choice to slightly (usually by + or - 0.25) over- or under-correct your sight. This is a decision best left to your eye doctor, I know nothing of the subject, but different methodologies used by different doctors may account for a discrepancy in different prescriptions given by them (in addition to the natural variability). Next time you may wish to talk to your doctor about this, and try out different lens strengths slightly above and below what (s)he recommended, to see what the effects are.

So, in conclusion, my advice to you is: go with that prescription, and live with it for a few months. See how you feel using your glasses - do you find yourself squinting a lot, do your eyes feel very tired after long stretches of different activities (eg computer use)? If you drive or cycle (or similar), can you read the roadsigns far enough ahead (this one is usually a good test of your eyesight) for you to feel safe? Most of all, though, do you feel comfortable with your eyesight? Take all this feedback back to your doctor next time you see him/her and discuss it. But, to be honest, with your eyes (my glasses are around -6.0, I'm blind as a mole without them!) there isn't much that can go wrong.

Hope this helps! — QuantumEleven 16:46, 16 November 2006 (UTC)

With the above disclaimers: I am not an eye doctor, but I have worn glasses for many years and I once slept in a Holiday Inn Express (reference to U.S. tv commercial). The sphere correction is minimal, but you have a stronger cylinder prescription to correct astigmatism. Without the glasses if you look at a vertical line and a horizontal line, you will likely notice one of them appears better focussed than the other. With the corrective lenses, they should both appear sharp. But you may find it takes a few days to get used to corrected vision; your brain is accustomed to the size distortion in the vertical versus the horizontal direction, so when you step off the curb (kerb?) and look down, there may be a moment of disorientation. Edison 17:31, 16 November 2006 (UTC)

Optometrists also "balance" your prescription needs between good near-focus and good far-focus. I discovered this when I complained to my optometrist that the correction I'd gotten from his last several sets of glasses wasn't very good. He then gave me a prescription that was purely aimed at correcting my distance vision (and damn my ability to use it for near vision) and the correction was remarkably better, but of course I have to take the glasses off a lot more to work up close. So be sure to tell your optometrist what your specific goals are.

And yes, they sometimes get it blatantly wrong or you gave a conflicting set of "better"/"worse" answers. This happened to me at least once.

Atlant 18:13, 16 November 2006 (UTC)

I went for a second opinion and got these results:

New Prescription		Sphere	Cylinder	Axis
Distance Vision	oculus dexter	+0.50	-0.75	180
	oculus sinister	+0.50	-0.75	015

The sphere for left eye is quite different!! --Sonjaaa 22:23, 16 November 2006 (UTC)

• Whenever I have my eyes checked, they ask me a series of questions about which lense views more comfortable. Part of the difference probably lies in your own input in the testing. Also, I wonder if both optometrists measured in the same way. Did they both test each eye separately and did a control to see if it would work with both eyes together afterwards? Did they test the pressure in your eyeball by blowing air into it? When you look into the distance with one eye. Do you see any discernable difference between left and right? Eyes tend to tire throughout the day, did you take both tests at approximately the same time in the day? Did you do something like watching a monitor or movie screen shortly before. I have worked at an store where I sold glasses and did basic measurements, but remember I can't give proper medical advice over the internet. By the way, eye tests can be done for free in the Netherlands if you don't suffer some serious eye illness (it saves a lot of waiting with a specialized eye doctor). If you want a third opinion, try a college/university that offers an optometrist's program. The students might need a patient for some classes. It might get you a free measurement. - Mgm|^(talk) 10:25, 17 November 2006 (UTC)

Call me paranoid, but I think that the optometric community is involved in a conspiracy to get everyone on glasses. Think about it:

• The conditions of the exam room - dark, difficult to see, designed for eye strain.
• Progressively stronger prescriptions weaken your eyes further; this causes increasing dependence on eyeglasses.
• Overprescription; have you noticed that new glasses seem excessively strong when you try them on for the first time?

My eye doctor screwed me; He prescribed glasses for 20/30 vision, and my vision has deteriorated since. Asshole. -- Sturgeonman 19:23, 19 November 2006 (UTC)

• Funny how people always see conspiracies. About one of your comments: "Overprescription; have you noticed that new glasses seem excessively strong when you try them on for the first time?" There's a perfectly logical explanation for this effect. Your eyes need to get used to wearing the glasses, because before they strained to see properly. If you do that when you put on those glasses it will feel like you're overcorrected, but that's due to your own eyes, not the glasses. Also, once your vision requires correction, it usually deteriorates, because your eye is not 100% healthy. If you want to get rid of eye doctors or glasses. Try getting laser surgery or practice those eye training exercises that claim to stop deterioration. I haven't tried those, but it can't hurt to try. - Mgm|^(talk) 12:54, 20 November 2006 (UTC)

Acarids

How come I can't find any information on acarids , acaridans on Wikipedia? Is it because they have another name? Keria 16:29, 16 November 2006 (UTC)

Is this it? Acarina If so, then somebody should create redirects to help ppl find it more easily. --Sonjaaa 16:38, 16 November 2006 (UTC)

Thank you very much - my dictionary gave me acarid as translation but it doesn't seem to be the usual term. Keria 16:41, 16 November 2006 (UTC)

It might not be the most common term, but it's not an unreasonable term to expect to work (many dictionaries, including wiktionary, have one or both names). So acarid, acarids, acaridan, and acaridans are now all redirects to Acarina. -- Finlay McWalter | Talk 19:01, 16 November 2006 (UTC)

Prothrombin time

Most articles trace the first description of the prothrombin time, discovered by Dr Armand Quick of Milwaukee, to a 1935 paper in J Biol Chem. I recently discovered that this reference does not in fact exist (as JBC is now available fulltext for free back to 1905). How could this have happened? JFW | T@lk 16:33, 16 November 2006 (UTC)

There certainly seems to be many references to that article, but there is another one of the same time with a similar title
Quick AJ, Stanley-Brown M, Bancroft FW. A study of the coagulation defect in hemophilia and in jaundice. Am J Med Sc 1935;190:501
It is odd that two nearly identical articles (at least judging by their titles) would be published the same year in two different journals.--Mabris 16:59, 16 November 2006 (UTC)

I suspect that it was a simple mistake (somebody knew they had read the article, but got the name of the journal wrong). However, since the journal was not available for free for people to verify this ref, they just took it on faith and replicated the error. This is a problem with sources that aren't readily available for free. Wikipedia should try to keep uses of such refs to a minimum, because of just this problem. StuRat 19:02, 16 November 2006 (UTC)

I am shocked, SHOCKED I say, that generations of scientists would cite a paper without having actually read it. Edison 22:56, 16 November 2006 (UTC)

Err cough cough. How long exactly have you been a scientist? 8-)--Light current 02:30, 17 November 2006 (UTC)

I once went to the library of a major research university to look up a much-cited paper in a journal from 1905. In the binding process, the edges of the pages of the issue were not slit apart. It had never been opened. Perhaps it was read via the Sleep learning method [9] of Edgar Cayce all the times it had been cited by scientists at the school.Edison 03:51, 17 November 2006 (UTC)

Future geography

I've seen maps of the Earth's original landmass, Pangaea, and its evolution as plate tectonics cause it to morph into the continents of the present day. Have geologists predicted what the Earth is going to look like in another several million years? Maps, predictions, or other opinions would be greatly appreciated. --Naferius 17:31, 16 November 2006 (UTC)

At Continental drift there is a link [10] which shows the continents, past and future. Edison 17:34, 16 November 2006 (UTC)

However, note that Pangaea is not the original land mass, as the supercontinent cycle has repeated itself many times over the Earth's history, causing various continents to join, then break apart again. We can trace back through the last several cycles. StuRat 18:47, 16 November 2006 (UTC)

Since the continents are destined to jam together again, and maybe break apart at different places, we can only go so many (hundred) million years in the future. --Zeizmic 21:38, 16 November 2006 (UTC)

To put this in perspective, the oldest map on that site is from 650 million years ago. So it only covers about 15% of Earth's history. Does this mean that nothing is known about the location of landmasses before that (only that they existed)? DirkvdM 09:12, 17 November 2006 (UTC)

The farther back we go, the fuzzier the info gets, yes. StuRat 09:53, 17 November 2006 (UTC)

The link is great - I wonder how the plates cause the continents to start in the southern hemisphere, and drift to the position where they are now, with the majority of landmass, ignoring Antartica, being visibly in the northern hemisphere.

The driving force is convection cells, where the core of the Earth cools itself by causing the mantle to "boil". The continents then move on these cells, similar to how scum on the top of a pot of boiling milk moves around. StuRat 20:27, 17 November 2006 (UTC)

And we're the scum that lives on top of that scum. DirkvdM 06:41, 18 November 2006 (UTC)

Makes me feel so desired in this universe. --Naferius 14:59, 18 November 2006 (UTC)

Diabeties

Can people get diabeties from eating meals too far apart? For example having breakfast at the normal time but then not eating until late afternoon?

--213.106.15.82 19:23, 16 November 2006 (UTC)

I don't think that could cause diabetes, but could make the symptoms worse if you are diabetic or pre-diabetic/hypoglycemic. A large number of small meals is typically recommended for such people, to keep their blood sugar as constant as possible. StuRat 19:38, 16 November 2006 (UTC)

No. No. alteripse 21:11, 16 November 2006 (UTC)

I have never heard of a direct causal mechanism for diabetes being meal timing. There may be some indirect effect wherein meal timing gives rise to greater caloric intake, thus it leads to weight gain and precipitates the onset of type II diabetes. So maybe, in an indirect way, but I can't think of a direct pathway. --TeaDrinker 21:38, 16 November 2006 (UTC)

for psychiatrists

What happens if a person who doesn't have any psychotic dissorder like schizophrenia starts taking neuroleptics and antipsychotics? does that person have a risk of actually developing schizophrenia if without taking that medicine that person was not destined to have the illnes develop ever at all?.

do other psychiatric medicines like antidepresants and axiety/epileptia pills like rivotril also have the posibility of triggering schizophrenia or any other dissorder like bipolar dissorder or multiple personality or whatever?.--Cosmic girl 22:27, 17 November 2006 (UTC) (sorry I forgot to sign it).

Miscellaneous side effects without beneficial effect. No. No. alteripse 21:10, 16 November 2006 (UTC)

I don't believe antipsychotics will cause a disorder like schizophrenia in a normal person, but it is definitely not considered safe for a person without a disorder to take any drugs which alter brain chemistry, especially long term. Taking medication or recreational drugs which create imbalances in brain chemistry (seratonin, dopamine)may make changes which are irreversible. This is a field which is still activley being researched. Vespine 22:10, 16 November 2006 (UTC)

If you read carefully the patient leaflets on these mind altering drugs, you will see that some of the side effects they can cause are actually the same as the condition for which they have been prescribed! THis also applies to some other types of drugs in my experience.--Light current 23:20, 16 November 2006 (UTC)

As a chemist (not psychiatrist) the answer is yes (or they may cause another mental illness that would not develope without the drug use.) The effects may or may not be permanent. Other possible side effects are mental retardation (for the period of use) and unknown long term effects - the only way to find out is try it.

As to the second question - antidepressant use can cause depression. You mentioned rivotril - I don't know much about this personally but the rivotril article states it is a benzodiazepine derivative - you could read that article for some clues..

Sorry, I disagree with some of the above answers, or at least the opinions need some support. Can anyone cite any evidence that antipsychotics can cause schizophrenia in someone not predisposed? I didnt think so. And I suspect the anonymous chemist is confusing tardive dyskinesia with mental retardation. alteripse 02:41, 17 November 2006 (UTC)

Antipsychotics can cause psychosis it seems - I didn't specifically mean schizophrenia - psychology is a strange subject if you ask me - explaining a predisposition to an illness or lack of it seems complex. Tardive dyskinesia may be all you see when observing someone on certain antipsychotics but I would suggest that the 'lights have been turned off' or at least dimmed as well. Please take me on my word that these drugs are not something you should give to people.

so psychiatrists are assholes?.--Cosmic girl 22:31, 17 November 2006 (UTC)

Not according to me.. Prescribing poisonous drugs is the bit I object to... Most psychoactive substances are poisonous - if you think about it - that includes medical drugs as well as recreational drugs. I'm not in a position to attempt to take the moral high ground here.

In my experience (one psychiatrist i met) - they were not keen to have to prescribe drugs - and who would be.. Remember one of Confucius's sayings "the best doctors have no patients" - in some way prescribing a drug means failure.

This is Tom Cruise-type nonsense masquerading as answers. All drugs are "poison" at some dose. No doctor or reasonable person thinks taking an antipsychotic could have no bad effects. You haven't offered evidence against either of my points: (1) antipsychotics can produce unwanted effects ("side effects") for anyone who takes them but (2) have not been shown to cause either schizophrenia or mental retardation in anyone. I will add a third: (3) they are no more dangerous to people without schizophrenia than with schizophrenia, but there is simply no potential beneficial effect to make the unwanted effects worthwhile. alteripse 01:40, 18 November 2006 (UTC)

thanks - no idea what 'tom cruise type nonsense' is but it sounds bad. My point is that these drugs are poison at any dose. Haloperidol " Depression, severe enough to result in suicide, is quite often seen during long-term treatment" Phenothiazine - "tardive dyskinesia and sedation" - sounds to me when in combination like mental retardation. Read the side effects section in a wikipedia article of any drug used for mental disorders and then try to prove to yourself it's not a poison. Your third point is a good one but 'no more dangerous' is not good enough for most people. Not dangerous would be acceptable. Somebody asked about anxiety drugs "triggering schizophrenia or any other dissorder like bipolar dissorder or multiple personality or whatever" - in the worst case withdrawal from benzodiazepine can trigger psychosis - can you distinguish between schizophrenia and psychosis? (rhetorical question). Apologies for winding you up.

OK, I am unwound. Schizophrenia and psychosis are disabling problems that can prevent a person from holding a job, maintaining a place in the community, or maintaning relationships with the people important to them. Antipsychotics can help some of the people with these problems to hold jobs and maintain relationships. It is demeaning and insulting to people with mental illness when people with no experience, no stake, or little knowledge pass judgement on what treatments should be allowed or the motives of those who are trying to help, but offering little more than "think positive" or "snap out of it". Lots of drugs used for many conditions cause side effects, but they are often the least bad choice available for bad problems. alteripse 04:41, 18 November 2006 (UTC)

(I'm no MD) If you read the list of side effects and cautions for specific medications, classes of medications, or types of medications (like [[11]], you'll see that antidepressants can cause hypomania or mania (the opposites of depression), as well as numerous other side effects. Neuroleptics/antipsychotics can cause, among other things, akathisia and/or dysphoria. While they may not cause the illnesses you are asking about, they can cause many of the symptoms of those illnesses. --Ronz 05:26, 20 November 2006 (UTC)

Meals for humans

Is the human body designed to require feeding 3 or 4 times a day. Or do we do it just to stop ourselves feeling hungry?--Light current 23:29, 16 November 2006 (UTC)

I do recall that we are supposed to eat about six "snack-like meals" a day instead of three big meals... Cbrown1023 00:15, 17 November 2006 (UTC)

It is recommended to eat little bits, more often, throughout the day, rather than a whole lot in just three meals. --Russoc4 00:24, 17 November 2006 (UTC)

From Human Evolution: "Early hominoids, like apes, were essentially plant eaters (fruit, leaves, roots), their diet only occasionally supplemented by meat (often from scavenging)." We evolved from chimpanzee-like animals that generally ate several times during the day, and this is thus the best way to feed ourselves today. Dar-Ape 00:33, 17 November 2006 (UTC)

And who could question the authority of an ape on this subject? :) DirkvdM 09:18, 17 November 2006 (UTC)

None of which answers the question. Try these versions:

1. Most of us do not think the human body was "designed". If so, we have no direct information from the Designer as to an intended eating frequency.
2. "OK, what eating frequency did most early humans have?" We don't know. Anthropologists can tell all the just-so stories you like, and you can compare us to any ape you like, but we simply do not know. About all we know is that humans are amazingly adaptable in terms of what we can eat and how often.
3. "All right, then what is the healthiest meal frequency?" We have no controlled trials demonstrating that one frequency is better than another. For a modern sedentary lifestyle in an urban environment with American food abundance, there is some evidence that eating more earlier in the day and less later in the day is healthier. alteripse 02:35, 17 November 2006 (UTC)

Bravo! Can you make a template out of this answer for every "what is the proper..." questions? --best, kevin [kzollman][talk] 06:12, 17 November 2006 (UTC)

Do you mean you think that Alteripses is an 'ideal' answer? Yes its pretty good as it answers fully the question asked and the question that should have been asked! Yeah Ill give it 8/10. --Light current 11:04, 17 November 2006 (UTC)

You mean a big breakfast, light lunch and modest dinner? (maybe with snacks in between? 8-))--Light current 02:38, 17 November 2006 (UTC)

Some Wise Man (Ben Franklin?) said "Eat breakfast like a King, lunch like a prince, and supper like a pauper." And most people who say "I never eat breakfast" in fact eat it about 11 pm.Edison 03:54, 17 November 2006 (UTC)

I always sort of compared my eating late at night with others eating breakfast (I don't eat "breakfast"). However, I do believe there's research saying several small meals is better than 3 big meals, but I don't know why people don't advocate it. It's better for the metabolism, weight, etc, so I know it's recommended to some people who are trying to lose weight. I always just followed what my body tells me, which is eating more often in a day, but not eating so much at each "meal", and I guess there's some biological studies backing that habit up. The 3 meals thing has to be invented by society. All the pets I've had (save one) also always had food out, and when you do that (considering they're not gluttons), they eat at random times in the day. I didn't realize that till just 5 minutes ago, but that could be some sort of proof that we're just supposed to eat when we're hungry and not so much during meals, which also cuts out the notion that you have to eat a lot at each meal to last till the next one etc. --Wirbelwindヴィルヴェルヴィント (talk) 09:23, 17 November 2006 (UTC)

So maybe you should just eat enough to satisfy the hunger pangs and not so much that your are stuffed full? 8-)--Light current 10:45, 17 November 2006 (UTC)

Different cultures eat on entirely different meal schedules. In the US we usually have a small breakfast, medium lunch, medium dinner; in Brazil, if I recall, you have a small breakfast, huge lunch, small dinner. The human body is remarkably resilient to adapt to different types of eating, which makes sense: in the wild, one does not always get to choose exactly when and how much one eats. If one were locked into a "eat one way or suffer horribly" sort of cycle one a civilization would not have the flexibility to do the sorts of things that humans have done (like migrate across arid lands). --24.147.86.187 13:45, 17 November 2006 (UTC)

Yes but it does appear the humans eat 3 or 4 times a day over the world. How did we get to that? Was it found by trial and error that if this pattern is followed, we do t get too hungry?--Light current 16:40, 17 November 2006 (UTC)

science fair project

what type of trees make money? where are the trees located? email removed

money is made of cotton... see Banknote#Materials_used_for_banknotes. Cbrown1023 00:14, 17 November 2006 (UTC)

"Money on trees" is just a cliche. Though I'm sure a lot of people wish it was true! --Wooty  Woot? | contribs 01:33, 17 November 2006 (UTC)

I'm guessing they are asking which types of trees are profitable to grow. There are fruit trees, and trees used for lumber, and others used for their sap (to make rubber or maple syrup). Some lightweight wood has special uses, like cork, balsa, and bamboo. Some tree leaves can be woven to make baskets. Particularly large, old, or unusual trees may make money by tourism. Other trees are only suitable as firewood. StuRat 02:33, 17 November 2006 (UTC)

Pulpwood for paper, nut trees... -THB 04:05, 17 November 2006 (UTC)

Agarwood is expensive, and people make a lot of money from it, but its only a fraction of profit worldwide from the forestry industry. Something makes me think fruit trees are the biggest moneymakers worldwide, but that's just a guess. Lowerarchy 05:44, 17 November 2006 (UTC)

Marco Polo-era China used mulberry bark as currency; check this out:[12]-- Sturgeonman 19:13, 19 November 2006 (UTC)

November 17

Displacement of the Universe

When an object expands, it displaces something already there. If our universe is expanding, what is it displacing?

Is the universe an object? Melchoir 00:27, 17 November 2006 (UTC)

I would suggests that as it expands - it creates space - there for it displaces nothing. (any good?)

The universe is by (one) definition everything, so there is nothing outside it to be displaced. The problem here is that space as we perceive it in everyday life is not the same as what is at play here. Don't ask me to explain that, because it baffles me too. DirkvdM 09:32, 17 November 2006 (UTC)

My view is that space does not exist without mass. 8-|--Light current 16:36, 17 November 2006 (UTC)

I thank you for your answers; however, I do suggest that the universe is an object and that, as it expands, it has to displace something that is there. Does this mean that there is another universe?

No, it means your beliefs are not consistent with modern physics. — Knowledge Seeker দ 03:56, 18 November 2006 (UTC)

Which also goes for all the great scientists, but that's no guarantee .... :) DirkvdM 06:59, 18 November 2006 (UTC)

Like I said, there is by definition only one universe. When physicists speak of the universe they mean 'everything there is'. The word 'object' is a bit vague. I suppose you mean 'entity', which is really a mental construct (as is 'object', in a sense, for that matter) - whichever you wish to see as one whole is therefore an entity. Aanyway, I had a similar notion, but my conclusion was that the size of the universe is by definition fixed. The expansion of the universe is sometimes illustrated with a balloon with dots on it. When you blow it up, the dots all move away from each other. In kosmology, we notice that everything around us is moving away from us (apart from local movements), so an explanation for that, the reasoning goes, would be that we're part of an expanding 'balloon' (the universe). But how do you know the balloon expands? Because you compare it to its surroundings (it may also be that the room you're in is getting smaller, but that would be too complicated an explanation). But for the universe there are no surroundings, so its size has to be given (a constant), unchangeable. This eventually led me to my alternative to the Big Bang theory, but I doubt if that will clarify things for you. :) DirkvdM 06:59, 18 November 2006 (UTC)

Jupiter Explosion

I was wondering when Shoemaker-levy 9 crashed into jupiter why didn't the planet Explode?

The short answer is that the combined mass of the parts of SL9 were insignificant compared to that of Jupiter.Bunthorne 02:03, 17 November 2006 (UTC)

However, if the mass of SL9 had been moving at a speed close to the speed of light relative to Jupiter, far more damage would have been done. Fortunately, such large objects seldom move at those velocities, within our solar system. StuRat 02:23, 17 November 2006 (UTC)

Do they outside our solar system? DirkvdM 09:37, 17 November 2006 (UTC)

I believe there are higher speed objects outside the solar system, like ejecta from supernovae, yes. However, these objects still only move at a small portion of the speed of light. StuRat 09:49, 17 November 2006 (UTC)

Nope, the fastest objects (I mean large objects) in the universe only move at a few thousand kilometres per second. This is below 1% of the speed of light. --Bowlhover 17:23, 17 November 2006 (UTC)

Perhaps you are thinking that the large quantity of hydrogen gas in the Jovian atmosphere should have ignited. This didn't happen because there isn't much free oxygen in the Jovian atmosphere, and oxygen is needed to burn hydrogen. StuRat 02:20, 17 November 2006 (UTC)

Could such a mixture exist for long anywhere? Any atmosphere would at some time have some sort of discharge setting it off, wouldn't it? Put differently, if such a mixture would start to build up, it would be ignited (again and again) before it ever accumulated to anything. DirkvdM 09:37, 17 November 2006 (UTC)

Yes, that's one reason why you only get free oxygen or free hydrogen in a planet's atmosphere, but never large quantities of both. StuRat 09:43, 17 November 2006 (UTC)

Greenhouse gases

What equipments must be need in order to measure the level of carbon dioxide in the air? How can you control the level of carbon dioxide? It is for a science project, so if anyone who know the answer to this question, please answer as soon as possible. —The preceding unsigned comment was added by 68.162.145.234 (talk • contribs) .

For many applications, you can use a CO2 sensor, however they tend to be fairly expensive (in the hundreds to thousands of dollars). This sensor works with a TI calculator CBL (calc. based lab) unit. You may want to ask if your school has some of these which they will let you borrow (or use in the lab). If you're working with very gross measurement (pure CO2 versus air), you could use a flame to distinguish them (a flame will not burn in CO2, since it needs O2).

You can raise the CO2 level of a containter by adding CO2. Dry ice is CO2, just put it hot water and vapor will come off. The vapor is a bit heavier than air, so you can manifpulate it by pouring the vapor into a container. This would not give you very fine control over the amount, of course. Lowering the CO2 level is a bit harder, since it is difficult to add a gas which is the same as air (O2, N2, trace gasses) excluding the CO2.

This seems like a fairly difficult project. What more specifically are you thinking of doing? --TeaDrinker 04:27, 17 November 2006 (UTC)

A cheap but slow and probably fairly inaccurate method might be to see how fast a plant grows in that air. Of course, you'd have to calibrate this first, measuring the growth rate in known CO2 concentrations. Or use such measurements done by others and recreate exactly the same circumstances. DirkvdM 09:49, 17 November 2006 (UTC)

Growth rates might be even more trouble, since there is natural variablity in plants. Thus it would be necessaary to grow multiple plants in the same environment and average their growth rate. It is further complicated by the CO2 used by the plants, since the conccentration will change with time. Consideration of soil type, light availablity, watering, etc. would make this a difficult measurement. --TeaDrinker 21:38, 17 November 2006 (UTC)

I think it's a novel idea. But it would only work while CO2 was the limiting factor in the growth of the plant. Note also that different plants take up CO2 with different mechanisms. E.g. see C4 carbon fixation. —Pengo ^{talk · contribs} 01:42, 18 November 2006 (UTC)

The other nutrients have to be standardised (that's part of the calibration), but that does not necessarily mean plentiful (although that will of course help). And it would have to be a very standardised plant (preferably all seeds being 'twins'), such as a highly cultivated plant. It would also help if it were a fast growing plant. Hemp comes to mind, but that might come with some legality problems. :) I suggest a narrow tube, barely wide enough to fit a seed in. Water at the bottom, with a standardised amount of nutrients dissolved in it, and air at the top, with the seed on the border between the two, possibly floating on a bit of oil (also to prevent the CO2 from dissolving in the water?), flooded in light (again standardised, so in a container to keep any other light out) and with an airtight lid on it. If the amount of air is very limited the plant will use the CO2 up quickly and stop growing at a certain point. The lenght of the seedling at that point (which can only expand in two directions because of the narrow tube, so the length is easily measured) is an indication of the amount of CO2. Do this a few times with known concentrations of CO2 (the calibration) and you've got an indication of the amount of CO2. Like I said, not too accurate and a bit slow (takes at least one day per sample), but cheap and easy. Oh, and you'd have to add some O2 (again, a fixed amount) to avoid that running out (which would be too limiting a factor :) ) That might be a bit more difficult (but not too difficult). Another option would be a clipping from one plant, but it would have to be a standardised type of clipping, which might pose a problem. DirkvdM 07:41, 18 November 2006 (UTC)

If you're looking for something cheap, I wonder if you could use Lime water and measure how cloudy it got? It might be tricky, and fairly inaccurate, to measure 'cloudiness' (maybe bubble the gas through a beaker with a sequence of marks underneath, of various 'blacknesses', and see which ones are still visible after a certain quantity of gas has passed through?). It should be doable with normal school lab equipment, though. Skittle 21:50, 17 November 2006 (UTC)

The cloudiness might be measured by shining a standard light source through it and measuring what passes through with a light sensor at the other side. DirkvdM 07:41, 18 November 2006 (UTC)

A photometer is a fairly common item. If your school has a photography class, they undoubtedly have light meters which may be useful in the manner suggested. --TeaDrinker 08:39, 18 November 2006 (UTC)

Targeted Drugs

What are some the barriers that are impeded the development of targeted drugs? Since we know a specific protein looks like, what it makes so hard to design a molecule that will interact with that protein? --Wedgeoli 03:48, 17 November 2006 (UTC)

Of course, there are still all the barriers that all drugs face, like extensive animal and human test trial requirements. StuRat 07:48, 17 November 2006 (UTC)

If you know what a protein looks like, that doesn't mean you know how it does what it does and what would stop it doing that (or whatever your goal is) and when you do know that, that doesn't mean you can make that stuff (economically). And then what StuRat said. DirkvdM 09:53, 17 November 2006 (UTC)

The configuration of a molecule has a huge effect on the interactions between molecules. Biologists can look at a protein and say, "It's folded this way, which produces this effect," but it's very difficult to do the reverse: "I want a molecule that does THIS, so it needs to be folded thusly." Look at Protein folding. Secondly, a single type of protein chain can do a lot of different things in an organism. If you target a "bad protein," you may also be inhibiting the protein in good functions. sthomson 16:59, 17 November 2006 (UTC)

Memory foam outgassing

Anybody know what the stink that emanates from memory foam is? Will I grow a third hand from my forehead? Clarityfiend 04:53, 17 November 2006 (UTC)

That might come in handy (excuse the pun) if you've got the Sun in your eyes. DirkvdM 09:55, 17 November 2006 (UTC)

Some ventilation might be a good idea. What is the object ? If it's a pillow, it's not going to be easy to avoid the fumes. StuRat 07:43, 17 November 2006 (UTC)

I developed a horrible skin rash when I first started using a memory foam mattress, though the jury's still out as to if it was the cause. I have no idea what the chemicals involved in the creation of the foam are, but they're probably not very healthy - I doubt they have significant mutagenic power, though. Most likely would probably be some nasal or dermal irritation. Virog^{It's not}_{my fault!} 08:43, 17 November 2006 (UTC)

It might be a good idea to let it outgas for a while in a garage or storage area, before using it. However, I suspect that flexing it will cause more fumes to be released. StuRat 09:38, 17 November 2006 (UTC)

Also, can you cover the item in a vapor-proof plastic ? StuRat 09:40, 17 November 2006 (UTC)

All new furniture and carpet has this problem. In office buildings they go through a special high-ventilation cycle for a while before allowing occupation. I'm quite sensitive to fumes, and didn't have any problems with my new Novaform mattress. Perhaps some manufacturers pre-ventilate? --Zeizmic 13:14, 17 November 2006 (UTC)

Any ideas/available products for simple intercom switch over POTS?

I'd like to rig something (if necessary) that can remotely communicate with a phone plugged into a POTS. The intercom system in my apartment building is a CC phone system. Visitors punch in my apartment number and my phone line rings. The thing is, I don't have land-line service (I use my cell phone), so this CC system is the only one accessible. Thus, a solution I have in mind would, by definition, not interfere with my usual phone habits.

I would like to have a small remote control (around the size of a car's remote keyless entry device) that I can clip to my belt. One button on this remote control would pick up or hang up the line. The triggered phone would be a speaker phone so I could talk without a handset. The other button would trigger the phone to send a touch tone signal and buzz the person in. So when the phone rang, I would hit the pick-up button, chat momentarily, hit the tone button, then hit the pick-up button again to hang up.

Does anyone know of anything like this available for retail? I thought that, if necessary, I could get one of those wireless doorbell things that supports multiple doorbell signals (for multiple buttons), and rig it to the phone somehow, but I'm not quite sure where to start.

Thanks! --Silvaran 05:37, 17 November 2006 (UTC)

Firslty Im not clear about your use of the word POTS. What you seem to have described is purely an intercom system for the building.

The first requirement could be met just by wiring a relay (in series with a holding coil) in parallel with the hook switch of your phone. THe relay would be activated by the remote (infra red, radio or, ultrasonic). THe phone would then operate as a speaker phone 8-).

For the second requirement you would need a tone generator to tbe connected to the line but not the telephone. Also at the front door, you would need a tone detector and solenoid system (if not already in existence) to operate the lock. One big problem is not interfering with other peoples intercom systems. Without a circuit diagram of the existing system , its difficult to say what the best solution is! 8-(--Light current 14:20, 17 November 2006 (UTC)

An electronics technician or electrical engineer could easily design a system to satisfy your needs. Please budget one man-month for preparing the proposal, designing and debugging the device, testing, and production of a final product in an attractive case, with user support. Edison 15:26, 17 November 2006 (UTC)

Exactly! I am available at cheap rates.! --Light current 16:11, 17 November 2006 (UTC)

The math is, two such qualified persons working together could have the device in your hands in about 2 weeks. Still one man month. Edison 23:07, 17 November 2006 (UTC)

The reason I said POTS is because it IS a plain old telephone system, not an intercom system. The panel at the front door stores code to phone number mappings (if you have phone service, you need to tell the superintendent your phone number so he can program it into the intercom system--you can even give a cell phone number if desired, but I didn't, for various reasons). When you punch in the code, you hear the ring-out. My phone rings (regardless whether or not I have service with the actual phone company), and I can hit 6 on the phone, the panel at the front of the building senses the tone and temporarily unlocks the door. So I want a speakerphone with a remote control that can pickup/hangup and hit '6'. :) --Silvaran 18:50, 17 November 2006 (UTC)

PS: I'm not sure exactly what gets programmed into the panel when you don't have phone service, maybe an arbitrarily-assigned extension number.

What you are describing is a system attached to the PSTN that rings your phone when someone presses your doorbell? So your number is programmed in and it autodials your phone number. THe front door lock somehow must also respond to you dialling 6 on your phone. Yes?

Ah Now slightly more complex. As I said pickup/hangup is (probably) no problem. You say the phone is tone dialling so you need a DTMF chip that will generate the dual tone for '6'. You connect the o/p of your remote control Rx to the '6' pin on the chip and send it through the phone microphone. You can do this easily if its a speaker phone. No need to wire stuff inside the phone. Tell me if I ve understood your problem correctly.--Light current 19:12, 17 November 2006 (UTC)

It is the "slightly more complex," that runs up the manhours to a high multiple of what you would at first expect. Edison 23:07, 17 November 2006 (UTC)

Yup that's pretty much it. If I get a barebones speakerphone and take it apart, is it somewhat reasonable to hook up some kind of remote control to it? (to the talk/hangup button on the speakerphone, let's say, as well as the 6 key). IR would likely be the easiest, though for obvious reasons, RF would be more convenient. Only thing would be choosing a simple remote control (maybe one of those pedestal fans with the remote controls), and then integrating the Rx thingy on the fan to the mechanics in the speakerphone (or PCB? Not sure when those became popular in phones). --Silvaran 19:25, 17 November 2006 (UTC)

Seems reasonable technically as long as the phones has got switches you can connect to. However, there may be some FCC or telephone company rules that say you cant connect anything you like (such as modified phones) to the telephone network without approval. We have such rules in UK --Light current 19:53, 17 November 2006 (UTC)

Well I'm not looking to violate any laws here (presumably I'm under CRTC jurisdiction here in Canada) and at the same time, my telephone jack isn't connected to the public telephone system. For the time being I'm going to grab myself a sub-$30 speaker phone and a cheap remote-controlled fan (which seems to have a minimal remote control that functions via IR) and see what I can make from that... with the right tools and some very, very careful (*cough* solder) modifications :). I appreciate everyone's input. I only wish I had the funds to support a more reliable development method (right Light current? :). --Silvaran 07:37, 18 November 2006 (UTC)

physics

Why weight(force) is expressed in mass units(Kg)?

Because mass is universal, while weight varies depending on the force of gravity in your location. StuRat 07:40, 17 November 2006 (UTC)

For historical reasons. The SI unit is the newton (N).  --Lambiam^Talk 08:28, 17 November 2006 (UTC)

Without acceleration, either in the form of gravity or in the form of a change in velocity, mass has no weight. Weight is a type of force. Force=mass times acceleration. Gravity produces an acceleration of about 9.8 meters/second squared, so a 1 kilogram mass acquires a weight of 9.8 kilogram meters per second squared, which is 9.8 Newtons at rest in earth's gravity. Weight is a vector force which is proportional to gravity and to mass. On Mars, where gravity is 3.3 m/s^2, the same object would only weigh 3.3 N. Edison 15:35, 17 November 2006 (UTC)

Weight should be expressed in Newtons. However, it's sometimes expressed in kilograms because it's easier to imagine. Not many people know what a newton of force feels like, but most people know how heavy a 1 kg object feels (since kg is a more well-known unit). --Bowlhover 17:11, 17 November 2006 (UTC)

Original research or not?

What strikes most people about Einstein’s equation is how much energy can be derived from such a small amount of mass. What strikes me is how little mass it takes to contain so much energy. How is this possible? What must energy and mass be doing that connects them by the velocity of light squared? Velocity is the same distance an object travels in the same interval of time while velocity squared is the acceleration or deceleration or the change in distance or direction an object travels in the same interval of time. If I hit the gas and go from 0 to 60 mph then my velocity will change at a faster and faster rate. Oddly enough if my velocity remains the same and I change my direction acceleration will also occur. Go figure! Mathematically acceleration can be represented by mass/distance traveled per unit time/distance traveled per unit time or the rate of change in velocity of unit mass. Since acceleration also occurs when the direction of travel of a mass changes a mass that is traveling at a constant velocity but say in a circle is accelerating. The directional vector of acceleration (not to be confused with the direction of travel of the mass) in the case of circular travel is at right angles to the direction of travel of the mass. Now consider that instead of the acceleration of mass we have the acceleration of energy. (is such a thing even possible?) i.e., energy/distance per unit time/distance per unit time. In other words energy traveling in a circle. According to Einstein’s equation then it would appear that matter is nothing more than energy traveling in a circle at the speed of light, i.e. energy/distance light travels per unit time/distance light travels per unit time. That is that mass is simply and profoundly energy (traveling in a circle) at the speed light. Adaptron 08:43, 17 November 2006 (UTC)

Technically, if you integrate velocity, you get $1/2*s^{2}$. If you hit the gas and go from 0 to 60, your velocity shouldn't change at a faster and faster rate unless your acceleration increases. Else it's a constant rate. If you change directions, of course velocity as a vector will change, but the magnitude doesn't change. And no, energy don't accelerate, and electrons do have a mass. But wait, what's the question? --Wirbelwindヴィルヴェルヴィント (talk) 09:11, 17 November 2006 (UTC)

In the above, with respect to what are you integrating velocity, and what does $s$ stand for?  --Lambiam^Talk 09:30, 17 November 2006 (UTC)

velocity. I think I recall learning physics using d, s, and a for distance, velocity, and acceleration, and v was used for something else. But I'm also an electrical engineer, and v was probably just replaced since it's used for voltages, just like I use "j" for imaginary instead of "i" (i is used for current). --Wirbelwindヴィルヴェルヴィント (talk) 21:42, 17 November 2006 (UTC)

Let's try to clarify to avoid any possible misunderstanding here. When you integrate velocity with respect to time, you get displacement. This is not usually the same as distance travelled. However, in the special case of an object accelerating from rest with a constant acceleration a, then the displacement (or, strictly speaking, the magnitude of the displacement vector) does happen to equal distance travelled, because in this case the velocity vector and the displacement vector are always parallel. In this special case, if velocity after time t is v then

$v=at$

$distance=|displacement|=\int _{0}^{t}v\,dt={\frac {at^{2}}{2}}={\frac {vt}{2}}={\frac {v^{2}}{2a}}$

(although this has become not very relevant to the original question). Gandalf61 14:08, 17 November 2006 (UTC)

Yes, it is original research unless you can cite a source. As far as I can tell (and I happen to know a bit about relativity) it is also a strange mix of speculation, incorrect statements, and phrases I can't parse at all. If you want to learn about relativity, please see the Introduction to special relativity. Do you have a question other than whether the above is original research? -- SCZenz 09:38, 17 November 2006 (UTC)

Is matter simply energy that is "locked" or "trapped" into circular or spherical direction at such a high velocity (i.e., the velocity of light which is beleived to have special effects on matter BTW, i.e., expansion) that energy in this state actually acquires all of the properties attributed to mass, i.e. gravitation, etc.? 71.100.6.152 11:27, 17 November 2006 (UTC)

Meh I stopped reading when, of the first three premises he states, the second is outright false (c² is in m²/s² not m/s²) and the third is not necessarily true (constant-acceleration, linear velocity increase is possible too). DMacks 14:08, 17 November 2006 (UTC)

How then does one account for such a large amount of energy being contained in such a small space? 71.100.6.152 14:56, 17 November 2006 (UTC)

Whoever said that energy has to take up space? You're incorrectly assuming that the concepts of objects and masses and kinetic energy as you're familiar with them from experiences on a macroscopic scale are the complete and true picture on all scales and for all more precise meanings. The Mass in special relativity page might be useful. DMacks 16:32, 17 November 2006 (UTC)

Excellent - "That is that mass is simply and profoundly energy (traveling in a circle) at the speed light" - but space is three dimensional so shouldn't that be a sphere? - If you can explain the 'motion' then I will surely give you a big prize. Keep up the good work...

Energy propagates in a linear direction (light for instance) as an electromagnetic wave which some think may be the result of a "leap frog" effect, if you will, of magnetism and electricity. Simply replace linear propagation with spherical propagation such as in a dog chasing its tail only with an infinitesimal circumference at the speed of light. (BTW please sign you comments.) 71.100.6.152 17:19, 17 November 2006 (UTC)

Thanks for your reply - but - the dog chasing its tail analogy is like a spinning disc and therfore still 2 dimensional - even if the circumference is reduced to infitessimally small or zero - please try again. Hope I have explained what I am asking for87.102.13.221 17:25, 17 November 2006 (UTC)

Think Ferret and spherical. However, at infinitesimal spherical circumference electric and magnetic lines of force may overlap the entire diameter of the sphere and exist and interact in lock step sufficient to be what we call mass. 71.100.6.152 18:26, 17 November 2006 (UTC)

I didn't really understand 'ferret and spherical'.

Ain't you never been in a pet shop where they have Ferrets on display??? Man you are missin' somethin'!. Them raskles can sure put on a show. Why they roll and turn and whatnot in so many different directions you can't see nothin' but a ball a fur. You need to get a life man. 71.100.6.152 19:39, 17 November 2006 (UTC)

Doesn't changing the orbital plane require a force acting in a direction other than "towards the center"? Centripetal acceleration would seem to keeps something moving only in a single flat circular orbit, so the analogy of someting moving "all around the center" (in 3D) is mis-applied I think. Again, relativistic physics and subatomic particle interactions are not just gravitational planetary motion or electrostatics writ small. DMacks 22:53, 17 November 2006 (UTC)

Humm... Seems like you are the one attempting to apply Newtonian to relativistic physics at the subatomic level. However, since acceleration is a vector force the directional might certainly deviate fron center or consider this: the center might thereby be constantly redefined. 71.100.6.152 20:31, 18 November 2006 (UTC)

As I understand it the 3d analog of 2d rotation is chirality? - anyone here who can expand on that?87.102.21.223 23:01, 17 November 2006 (UTC)

Levitating pens

According to Earnshaw's theorem, it should be impossible for a an array of permanent magnets to cause stable levitation. How then does the novelty magnetically floating pen and holder system work? --Light current 12:37, 17 November 2006 (UTC)

Add quote from page: This theorem also states that there is no possible static configuration of ferromagnets which can stably levitate an object against gravity, even when the magnetic forces are stronger than the gravitational forces. There are, however, several exceptions to the rule's assumptions which allow magnetic levitation. --Light current 14:08, 17 November 2006 (UTC)

What floating pen? Have you been drinking?

WP:AGF 8-))--Light current 14:04, 17 November 2006 (UTC)

He probably means something like this. They are a novelty pen for businessmen. --24.147.86.187 13:40, 17 November 2006 (UTC)

There is also gravity involved, besides the magnetic field. --Dementios.

I know gravity is involved! 8-)--Light current 14:03, 17 November 2006 (UTC)

Yes that link does show the sort of thing. especially the horizontal version--Light current 14:03, 17 November 2006 (UTC)

By the looks of things the magnets used are curved into a sort of cup and ball shape (like our shoulder joints) and there might be some magnets on the side of the inner bit which are helping stabalise it. I'd bet that the pen will only stay still if it is orientated a certain way (perhaps when you put the pen into its cradle it will spin to the correct position before it has time to fall over). Doesn't Earnshaw's theorem only work for magnets in a straight line (like MagLev), not curved magnets? RevenDS 14:07, 17 November 2006 (UTC)

It's possible that the pen itself is magnetic too, with the effect only working with pen aligned so that it has the same polarity as the magnets. Earnshaw assumed that all the forces involved were attractive, since this would cause positive feedback and drag the pen even the nearer the edge, causing even more feedback etc due to our good friend Inverse square law. Adding repulsive forces into the mix too means that you get some negative feedback, so the pen enters equilibrium. Laïka 17:12, 17 November 2006 (UTC)

Well yes Im pretty sure the pen has magnets in as well.--Light current 21:22, 17 November 2006 (UTC)

See Magnetic_levitation

These are all terrible answers. Earnshaw's theorem definitely does apply, no matter what shape the magnets are, and no matter whether they attract or repel. You can't do it. The pen in the picture isn't actually levitating, it's just standing on its point. —Keenan Pepper 05:23, 18 November 2006 (UTC)

Not quite true; diamagnetic materials such as Pyrolytic carbon can levitate in a constant field. Laïka 11:16, 18 November 2006 (UTC)

What about the horizontal one?--Light current 17:31, 18 November 2006 (UTC)

How do you create mass from energy?

So, how?

Collide two high energy particles together, and sometimes you get extra particles. JBKramer 13:49, 17 November 2006 (UTC)

Just get in your car and accelerate. Per Einstein’s Special Theory of Relativity, what we call energy and mass are two ways of measuring the same thing. Every type of energy has mass, and each mass is a form of energy. Energy = mass time the velocity of light squared. When you burn a liter of gasoline, the mass of the combustion products will be slightly less than the mass of the gasoline. The missing mass, (in an amount too small to measure with a lab balance), was converted into energy. The car, having accelerated, will have more mass than it had at rest. A truck with a 10,000 kg mass is accelerated from rest to 30 m/s. The increase in Kinetic energy=1/2 m*v^2, or 1/2(10000kg)(30m/s)^2=4500000 Joule. The amount of energy turned to extra mass in the truck is m=kinetic energy/c squared=4500000 Joule/((3*10^8 m/s)^2)=5*10^ -11 kilogram, or .00000005 gram, or .00005 microgram. That mass would be undetectable in a 10,000 kg truck, but it would be mass created from energy. Edison 16:01, 17 November 2006 (UTC)

Are you sayin' that by using fossile fuel we are not only making the Earth more polluted but heavier too or should we just blame the sun for sending us energy that will eventually make the Earth heavier too? 71.100.6.152 19:10, 17 November 2006 (UTC)

You can't make the Earth heavier without adding anything to it. That's true in relativity as well as common sense. —Keenan Pepper 05:28, 18 November 2006 (UTC)

Endothermic reactions? (Not sure, but seems to make sense.) DirkvdM 10:18, 18 November 2006 (UTC)

Why does spin-stabilisation work?

The article about it is so helpful it might as well not exist - Dammit 13:47, 17 November 2006 (UTC)

Gyroscopic action. See gyroscope. JBKramer 13:48, 17 November 2006 (UTC)

Should this article exist or be merged with gyroscope?--Light current 14:06, 17 November 2006 (UTC)

I assume the generic term is spin stabilisation (or is that 'gyroscopic action'?). A gyroscope uses it, so could be merged into it. But it's such a broad subject that it merits its own article. It is also used for some (most?) spacecraft and I wonder if that is meant by 'rockets', but that's a different thing. Or is it also used for rockets? Another example the stub mentions is bullets. And then there is the stabilisation of a bycicle by the rotating wheels (although I remember hearing that that is not really the reason a bike stays upright). Any more examples? DirkvdM 10:28, 18 November 2006 (UTC)

Prilosec (medical question)

I read the page on Prilosec already, but I had a question not answered there. I know I shouldn't be asking a medical question without asking a doctor and all that, this is more curiosity:

Why is it that when Prilosec was made available OTC, there are all sorts of warnings that it can only be taken for 14 days every 4 months. Does the doctor normally do some sort of liver/stomach test to see how you are doing on it? I know plenty of people pretty much take it once a day for years. Namlemez 15:22, 17 November 2006 (UTC)

I don't know about Prilosec specifically, but one of the usual concerns about anybody self-medicating for a long period of time is that they may be concealling or ignoring symptoms of some more-serious underlying disease (in Prilosec's case, such as an ulcer or stomach cancer).

Atlant 16:59, 17 November 2006 (UTC)

Also, increasing the pH of the stomach can allow microbiological growth. By alternating between periods of high and low acidity, gastric bacteria are less likely to grow out of control.Tuckerekcut 19:00, 17 November 2006 (UTC)

casimir like effects

Now i know that this effect is touted by any load of free energy nutballs out there that wanna make a quick buck, but have gone on the NASA site and found that they are looking into it seriously for propulsion [however they think tapping it for free energy is impossible and dangerous to even try]. According to a physics website on an article called "the casimir effect: a force from nothing" it claims that the zero-point energy field is pushing in on us all the time and that if enough of the zero-point energy field is imbalanced [so far as i understand by making the cavity between to plates unable to hold larger EM waves] the pressures on the outside of the mirrors or diveders is more than on the inside and the plates are pushed together. Apparently at micron distances apart the pressure is as much as one atmosphere [just over 1 kg per cm2] thats alot of pressure pushing in every direction, my first question is why do we not feel this pressure on us? secondly the casimir effect seems to suggest that the zero-point field acts almost like water or air pressure, [similar effect with imbalances of pressure] apparently NASA wants to create a method of propulsion that makes a certain area of the zero-point field resonate at a higher frequency thus more pressure on one side of the object, this pressure propells it. We can do the same with air and water [fans, airoplane wings, etc] What methods does anyone know of that could possible do this or are any known. The institute for advanced studies in Austin thinks that maybe a disturbance of the correct kind in the ground state of an atom would create such a resonance. Any othere ideas? Robin

The casimir effect has an excellent article on Wikipedia. JBKramer 16:24, 17 November 2006 (UTC)

You mean Wikipedia has an excellent article on the Casimir effect. :) DirkvdM 10:31, 18 November 2006 (UTC)

Indeed but while it says everything it says above in a longer and more scientific fashion it gives no hint as to other methods to cause energetic equilibrium distruptions of the kind i have mentioned and the kind that NASA are in search of. Robin

This is a reference desk. The article actually mentions other similar effects - waves and ships, for instance. If you want to talk about hypothetical zero-point energy generators, there are numerous message boards for such. JBKramer 18:30, 17 November 2006 (UTC)

I don't see how you could take advantage of a constant pressure to create movement. The examples you gave do not. A fan/prop uses supplied energy to move the medium. A wing converts forward thrust (provided by engines) into lift. So, in both cases, outside energy is needed, and that's what actually provides the propulsion. However, if there are waves or currents in this zero-point energy, then it may be possible to derive movement from these, like a feather blowing in the wind, water currents, or solar wind. Also, if there are differences in zero-point energy pressure from one point to another, that could possibly be used to move to the low pressure areas, but some other propulsion method would be needed to move to high pressure areas. StuRat 20:11, 17 November 2006 (UTC)

Feeling a cold coming on

I woke up this morning with the ominous sore throat associated with upcoming colds. Other than stock up on medicines, is there anything else I can do now that I know it's on its way? I won't be taking anything here as firm medical advice, but it probably isn't serious, just a little foreboding. Thanks. 70.50.103.86 16:48, 17 November 2006 (UTC)

Ginger is very good for cold symptoms.--Light current 16:55, 17 November 2006 (UTC)

I usually get a half-dozen of these feelings per year, before a real cold strikes. If you have the time, take a dose of ibuprofen, and go to bed for the day, and you should be able to fight off a half-dozen of these, before a real cold strikes... --Zeizmic 16:57, 17 November 2006 (UTC)

Some people recommend zinc lozenges to treat the common cold. Others feel that When left to its own devices, a cold will run a week to a week-and-a-half, but when aggressively treated, it will only last seven to ten days.

Atlant 16:57, 17 November 2006 (UTC)

No, no. Thats six of one and half a dozen of the other!--Light current 17:02, 17 November 2006 (UTC)

Eat,eat,eat,eat. That's the cure. Oh but if you've got a cold coming on maybe you don't feel hungry? Oh dear.

I second Zeizmic. The best thing you can do is help your immune system, and you can do that by sleeping (not just resting at home), eating healthy food (if you're hungry) and keeping well-hydrated. Also, I've sometimes had success with gargling with hydrogen peroxide, and flushing my nasal passages with hot(tish) salt water. Also, even though you may be already infected, practice good hygeine; wash your hands often with hot soapy water, and refrain from touching your mucous membranes. Anchoress 17:49, 17 November 2006 (UTC)

Linus Pauling advocated megadoses of Vitamin C, but I don't personally see any value in this approach. StuRat 19:35, 17 November 2006 (UTC)

Yeah but he died!--Light current 20:02, 17 November 2006 (UTC)

Yes, at age 93... --Anon, 23:30 UTC, November 17.

Raw garlic is supposed to be good for it too, since it naturally anti-bacterial / anti-fungal. In Eastern medicine, ginger helps because it has yang properties. Other Eastern beliefs include the white part of oranges, but I never found that to work. --Wirbelwindヴィルヴェルヴィント (talk) 21:36, 17 November 2006 (UTC)

A friend of mine swears the cure for a sore throat is to drink a little whisky, with a drop or two of honey added to it. One time, feeling a cold coming on, I tried her remedy. The next morning I wasn't feeling very good at all. She said I must have overdone it (which may have been true). I asked her what healing properties the honey added to the whisky, wondering what strange medical principle was at work... she replied "Nothing... it just makes the whisky taste better!" 192.168.1.1 3:20pm, 17 November 2006 (Hic!)

Honey does help allergies by introducing pollen into your system. One natural way of helping allergies is consuming locally produced honey. However, honey has to be medicinal if it never spoils (it kills most bacteria by crenation, according to honey). --Wirbelwindヴィルヴェルヴィント (talk) 01:59, 18 November 2006 (UTC)

In my own experience, stress and lack of sleep were often the precursors to infections such as tonsillitus and strep. Not sure of the common cold, but drinking fluids and getting plenty of rest never hurts. Edison 23:15, 17 November 2006 (UTC)

OK then.

• Lots of food,
• lots of liquid
• painkillers
• ginger
• garlic
• hot milk with whisky
• lots of sleep
• any more?>

--Light current 00:34, 18 November 2006 (UTC)

Yes, you'll need a twist of lemon! 192.168.1.1 5:14pm, 17 November 2006 (PST)

A good long soak in a hot bath relieves stress, achy muscles, congested respiratory tract, and helps you get ready for sleep. -THB 05:02, 18 November 2006 (UTC)

Self induced Insanity - is it possible?

Is it possible to make yourself insane by continuously acting as if you are all the time. This was an escape plan during WW2 from Colditz castle I believe (TV series).--Light current 16:54, 17 November 2006 (UTC)

Can you explain - what is "acting as if you are all the time". Please.

It means even when you think no one is watching (they are) 8-)--Light current 18:47, 17 November 2006 (UTC)

Are you sure this wasn't meant to send the german guards insane - it's having that effect on me>

It could have had theat side effect, yes. But German guards were not sent home, they went to the russian front instead where it helped to be insane. 8-|--Light current 19:15, 17 November 2006 (UTC)

Does this mean 'acting as if one is insane to make oneself insane"? If so - how does this help me escape from colditz? This is a total mystery.

Maybe one can be brainwashed to think that he is insane. Assuming self-brainwashing is possible, self-induced insanity would be very possible. Basically, if you constantly tell yourself that you are insane, then you will subconsciously believe that you are insane, and you will start to act insane...I think. Also, if the brain believes that insanity is necessary to survival, there is a good chance that it will self-induce it...I think. Anyway, this is all speculation. Studying the works of Freud could be helpful. --Naferius 17:41, 17 November 2006 (UTC)

If British officers went insane the Germans would take pity on them and send them back to Britain on sick leave! Strange but true! 8-)--Light current 18:53, 17 November 2006 (UTC)

Studying Freud could be helpful if you want to know the answer, or if you want to become insane?

Anyway, this sounds very doubtful to me. In the United States, it's forbidden to execute the insane; the claim is that it's "cruel and unusual punishment" if the convict doesn't understand what's going to happen and why. (I'm against the death penalty, personally, but I've never followed the reasoning there -- seems to me that knowing what's going to happen, and why, is a major part of the cruelty of it.) Anyway, as far as I know no one has managed to make himself insane to take advantage of this. The closest thing that's happened is that prisoners on anti-psychotic meds will refuse to take them, hoping to become too insane to execute, but that doesn't work unless you need the meds in the first place. --Trovatore 17:52, 17 November 2006 (UTC)

Just wondering if it is possible to become a genius by brainwashing myself :-) --WikiCheng | Talk 18:12, 17 November 2006 (UTC)

"... and then I decided I was a lemon for a couple of weeks. I kept myself amused all that time jumping in and out of a gin and tonic." - Arthur cleared his throat, and then did it again. - "Where," he said, "did you ...?" - "Find a gin and tonic?" said Ford brightly. "I found a small lake that thought it was a gin and tonic, and jumped in and out of that. At least, I think it thought it was a gin and tonic." (LTAE) -- 201.48.104.76 18:17, 17 November 2006 (UTC)

Erm..no. That requires intelligence and education primarily. But you can make your mind more receptive to learning by self hypnosis. 9-)--Light current 18:49, 17 November 2006 (UTC)

I can't help but think of Hamlet. For those who haven't read it (or only scanned the notes), when he is confronted with the idea that he may be crazy (since he was talking to his father's ghost), he wonders if he is crazy or if he is just acting crazy. If he is just acting, will it end up that he is to be crazy. To be or not to be. So, you can see that this is not a new question and - coming from so long ago - I doubt it is one that can be answered. --Kainaw ^(talk) 19:47, 17 November 2006 (UTC)

Hmmm! 2B or not 2B That is the question eh?--Light current 19:55, 17 November 2006 (UTC)

A psychology professor said that in several cases in the mid 20th century a sane person had him/herself committed to an insane asylum to do investigative reporting, to get material for a book, or to investigate conditions inside for the government. In each case, within a day or two they decided that their families, co-workers or bosses had actually had them committed for real and no one would be getting them out after a short stay as planned. The point was that if you weren't insane when you went in, you would be shortly. That was a few years back. Now mentally ill people generally get put on powerful antidepressants, antipsychotics, or other psychoactive drugs, and once they are stable they generally get discharged in a very few days. There have been novels where someone decides to pretend he is insane, but turns out to really be insane., The implication is, if one decides to act as if he is insane, well maybe he is. The counterexample would be "crazy like a fox" as when a mobster pretends to be senile to avoid being tried. Edison 23:23, 17 November 2006 (UTC)

The pretend to be insane and go insane was not from Colditz the prisoner of war camp but from Colditz (TV series). See how easy the reality barrier breaks down? meltBanana 23:39, 17 November 2006 (UTC)

Yes I know it was from the TV series. What do you think I am -- insane? 8-)--Light current 00:24, 18 November 2006 (UTC)

It is still a mystery if Rudolph Hess really was crazy or just pretended to be. I believe he started acting ever stranger, so it might be that it was an act that made itself true (self-fulfilling behaviour?). DirkvdM 13:16, 18 November 2006 (UTC)

Transmission of infrared, light and others

Does someone know why:

• steel blocks light but not infrared,
• vacuum blocks infrared conduction and convection.
• glass blocks UV but not visible light
• ...

?

Why do some materials block specific kinds of electromagnetic radiation? Mr.K. 19:50, 17 November 2006 (UTC)

Steel reflects light and infrared? Infrared does not go through steel.

Vacuum allows infrared through - there's not convection because there are no gases in a vacuum to convect.

Vacuum allows infrared radiation, but not conduction or convection. Mr.K. 20:11, 17 November 2006 (UTC)

Third question more difficult...

But, this is not the point. The point is why.Mr.K. 20:12, 17 November 2006 (UTC)

OK first point - not true - no answer then.

second point - both conductance and convection depend on the matter conducting and convecting - in a vacuum there is no matter - hence no conduction or convection.

Still no answer to yuor third point.

See reflectance transmittance and absorbance--Light current 19:59, 17 November 2006 (UTC)

Well, it does not tell why steel absorbs light but glass do not. —The preceding unsigned comment was added by Mr.K. (talk • contribs) 20:13 18 November 2006 (UTC)

The article doesn't, but following some links does. In a nutshell, steel has a better absorption than glass at visible frequencies. Virog^{It's not}_{my fault!} 20:25, 17 November 2006 (UTC)

See plasmon frequency--Light current 20:30, 17 November 2006 (UTC)

Your example about vacuum is unrelated: conduction and convection are not forms of radiation, but rather behaviors of matter. Vacuum, not being matter, doesn't participate. As for electromagnetic radiation, and why opacity is frequency-dependent, for metals see plasma frequency and for other solids see band theory. In short, different varieties of light have different energies per photon and thus interact differently (or, in some cases, not much at all) with the electrons in a substance. Alternatively, you can talk about how well the electrons can absorb energy delivered at a certain frequency, considering the incoming light to be continuous. In a metal, below its plasma frequency, the electrons move so well with the incident light that they reflect it nearly perfectly; in many other solids, only certain energies of photons can easily be absorbed and propel an electron into a higher band. Does that help? --Tardis 20:50, 17 November 2006 (UTC)

This plasmon theory is new to me - I've been explaining reflectance and other properties of metals (as well as other solids) using band theory for a long time - plasmon theory seems little more than a extension of band theory - (just poking my nose in)

You should be able to find pictures taken at different wavelengths. For example, microwaves are stopped by glass (meaning if we see in the microwave spectrum, glass will look like a solid wall that lets nothing through). On the other hand, if you take pictures in the x-ray wavelengths, it goes through human flesh and takes lead to stop, and I'm sure you've seen x-ray photos. But yes, plasmon frequency is where you'd want to look. --Wirbelwindヴィルヴェルヴィント (talk) 21:32, 17 November 2006 (UTC)

If microwaves are stopped by glass, how am I able to cook food in a covered glass dish in the microwave oven?Edison 23:26, 17 November 2006 (UTC)

Microwaves are not stopped by glass. Thats why you need the metal mesh in the door!--Light current 00:26, 18 November 2006 (UTC)

Oops, I must have remembered wrong, or was taught wrong. "The cooking chamber itself is a Faraday cage enclosure which prevents the microwaves from escaping into the environment. The oven door is usually a glass panel for easy viewing, but has a layer of conductive mesh to maintain the shielding. Because the size of the perforations in the mesh is much less than the wavelength of 12 cm, the microwave radiation can not pass through the door, while visible light (with a much shorter wavelength) can." --Wirbelwindヴィルヴェルヴィント (talk) 01:52, 18 November 2006 (UTC)

Correct!--Light current 02:14, 18 November 2006 (UTC)

Sugar mites?

I keep finding tiny (less than 1mm width, maybe 2mm length) creatures in my sugar bowl - they're pale cream color. What are they, where are they coming from?, how do they get in the bowl? I clean it out and they're back in a few days - how do they find it - can they smell sugar? (The bowl has a lid but they still get in). Is it possible for a creature to exist entirely on white sugar?. They are very small but look a bit like a louse or tick...

Don't know about why they are there but they might have came back because the original mites laid eggs. I suppose you could soak the bowl in some kind of detergeant to rid the bowl of life. RevenDS 21:38, 17 November 2006 (UTC)

Tried that - also found them in plain flour in cupboard but not wholemeal flour, caster sugar or brown sugar - also in same cupboard and left open - maybe I should just move house.

Sounds like some type of weevils. Try the following procedure:

1) Toss out any food they've infected. Be sure to seal the garbage so they can't crawl out. You could also flush them or burn them in a fireplace. (This especially helps get out your frustration.)

2) Clean any containers they've infected with bleach, inside and out. Don't let the bleach sit in any metal containers, or it will cause corrosion.

3) Clean your shelves with a bleach-soaked sponge.

4) Lay borax down on the shelves. They don't like borax. Baking soda also works.

5) Make sure everything is stored in airproof containers, such as sealed Tupperware. A container with a lid that just sits on the top, like the typical sugar bowl, is not sufficient, it needs to seal. Unopened containers are normally, but not always, sealed. Some pasta (spaghetti, mac & cheese, etc.) isn't sealed even when unopened, however. Once opened, the bugs can always crawl in. If you don't have enough sealable containers, you could also store opened cereal, sugar, baked goods, etc., in the refrigerator or freezer.

If you are wondering, the bugs probably came from something you bought that already had bugs in it. I had the same type of problem, and this method worked for me. StuRat 22:24, 17 November 2006 (UTC)

Thanks - they don't look like weevils though more like lice (I'm no expert). Obviously I've got rid of the infected food and cleaned. I am worried about eggs though. They definately are not wheat weevils though unless an albino form exists - the head is too small as well. Most of them were in the flour though.

I'd still be interested if anyone could pin down exactly what they were..

Could they be ants, for example pharaoh ants?  --Lambiam^Talk 07:52, 18 November 2006 (UTC)

Definately not ants - legs too short.

They probably have three segment - the tail (abdomen is a least half the body length) they appear flattened compared to ants and the thorax/abdomen connection is quite broad (a bit like an earwig but without the tails - also much smaller and cream coloured) The head is too small to comment on.

Then perhaps booklice (picture)?  --Lambiam^Talk 14:16, 18 November 2006 (UTC)

No wings as in the image on the wikipedia page - but the supplied image is very similar - mine are (or hopefully were) much paler - the image is quite close to what they looked like - still possibly with less of a waist - less fat and slightly more flattened - legs might have been shorter - possibly underneath the body. Thanks.

Nymphs are often light-coloured compared to adults of the same species; I wonder if what you're seeing is the nymph stage of a familiar insect? Anchoress 21:53, 18 November 2006 (UTC)

Steel

This is just a request for someone to write an article on Chrome-vanadium steel. I was suprised I couldn't find one as it seems to be used in many hand tools. Obviously I haven't got the expertise to do this.

It's a variety of stainless steel, which we do have an article on. --Robert Merkel 22:04, 17 November 2006 (UTC)

It's not - chromium content is much less than 10% more like 1%, plus the article has nothing on it. Typicaly they are chrome or nickel plated to prevent corrosion - surely no neccessary for a >9%Cr steel? I'd also like to ask about S2 steel as well.

Looks like youve got more knowledge than we have ATM. So why not start an article on it?--Light current 22:48, 17 November 2006 (UTC)

What you can see above is honestly about the limit of my knowledge - other than 'Chrome vandanium steel is an alloy used in tools such as screwdrivers and spanners' I couldn't say much more. Maybe someone else will turn up.

skin necrosis

How long does it take to manifest when the cause is lack of bloodflow? and what is the maximum of time after which it will not present itself? or can it develop nonths or years after the trauma that cuts veins and blood vessels that supply blood to the skin? (going progressively from pink, to red, to purple, to black?).--Cosmic girl 22:22, 17 November 2006 (UTC)

Did you know that one treatment is using leeches to suck the excess blood out ? StuRat 22:29, 17 November 2006 (UTC)

I thought the condition was produced by lack of bloodflow, not by an exess of blood. --Cosmic girl 22:41, 17 November 2006 (UTC)

As I understand it, the broken blood vessels do allow blood to flow in, because of the higher blood pressure that arterial blood has (having just come from the heart). However, the lower BP in the capillaries and the resistance due to the broken blood vessels combine to prevent the blood from moving out as fast as it moves into the area. Thus, the blood pools, and the blood cells die. This causes the color changes you mentioned above. Leeches can increase the rate at which blood is removed, to match the rate at which it is supplied, giving the blood vessels time to heal. StuRat 01:25, 18 November 2006 (UTC)

See frostbite gangrene etc (if you must). Im not going to look! Ugh puke 8-((--Light current 22:45, 17 November 2006 (UTC)

Then there's also necrotizing fasciitis, don't worry, no pictures. X [Mac Davis] (DESK|How's my driving?) 01:26, 18 November 2006 (UTC)

The few instances of necrosis I've seen have presented after a few days from the initial insult. Not sure what all this blood flowing in business is about. Necrosis results from lack of oxygen to the cells. Lack of oxygen may be due to obstruction to blood flow or lack of oxygen in the blood. If you prevent blood flowing out you can increase the pressure in the tissues above the capillary perfusion pressure and therefore this is merely another cause of obstruction to blood flow.Mmoneypenny 16:36, 18 November 2006 (UTC)

November 18

note

the actions of refdeskbot appear to be hiding certain edits from the edit history annoyingly - I've left a message for the operator. This didn't use to happen (everything was better in the old days). Please delete this message one problem is resolved..— Preceding unsigned comment added by 87.102.21.223 (talk • contribs)

Message left at user's talk page in response. This is normal behavior for the bot, but is, I'm sure, open to some forms of discussion. Martinp23 00:38, 18 November 2006 (UTC)

I've left a message on your talk page. Suggesting archiving stuff that does not appear on the main (current) page. Current bot behaviour is wrong - if material on the main page is edited it should appear in the main page edit history.

Please see http://en.wikipedia.org/wiki/Wikipedia_talk:Reference_desk#refdeskbot Thanks87.102.21.223 01:04, 18 November 2006 (UTC)

The Moon

Is there anyway way to find out what some resources on the moon might be and how much of them is there? I checked the article if it's there I missed it.67.126.131.137 01:58, 18 November 2006 (UTC)

Is rock a resource? How about vacuum? --Wirbelwindヴィルヴェルヴィント (talk) 04:10, 18 November 2006 (UTC)

It depends on what you mean by resources. If you are talking about water, there is a smal possibility that some water ice exists in the permanently shadowed areas of large polar craters. Other than that, it depends what you need. All the chemical compositions or roacks and such are discussed in the main article. pschemp | talk 04:46, 18 November 2006 (UTC)

See Moon. StuRat 04:40, 18 November 2006 (UTC)

Ah I overlooked composition but one more thing, Which of these elments could be used as radiation shielding?

Lunar regolith has a number of uses. Since it's primarily made of oxides, there's potential for it to be used for in-situ oxygen generation. Some research has calculated that about 1-2 meters of regolith will provide ample shielding from radiation PDF. And apparently it can be utilized for a sort of concrete (like any rock mixture, I suppose). A good site to check out would be NASA's Centennial Challenges - there's a few there devoted to regolith mining and utilization. (Disclaimer: I'm involved in a team working on one of them) Virog^{It's not}_{my fault!} 07:55, 18 November 2006 (UTC)

The best evidence indicates Wensleydale as a major resource. B00P 08:56, 18 November 2006 (UTC)

As for radiation shielding, pretty much anything will do provided you have enough of it, though as I understand it hydrogen or simple hydrocarbons such as polyethylene are the best for cosmic ray protection on a mass-constrained spacecraft, and, unfortunately, hydrogen is very, very rare on the moon. But if you're building a static radiation shield on the moon itself, just pile up the moonrock as is. It'll be fine for the job. --Robert Merkel 10:37, 18 November 2006 (UTC)

Thank for all the information, Wensleydale sounds good.

I have read research saying that the lunar dust is similar to Portland cement, in that if you mix it with water it sets up like concrete. If water were extracted from the polar region, structures could be build in situ which would provide radiation shielding and protection from meteor impact, much cheaper than bringing structures and building material from Earth. There is also abundant solar energy (never a cloudy day).Edison 21:55, 18 November 2006 (UTC)

Highest and lowest temperature and pressure

What is the highest temperature that could be obtained artificially? What is the highest pressure that could be obtained artificially? What is the lowest temperature that could be obtained artificially? What is the lowest pressure that could be obtained artificially?

Thank you.

For low pressure, see Ultra high vacuum, and even though you didn't specifically ask for low temperature (you asked for high temperature twice), see absolute zero for that. —Keenan Pepper 05:14, 18 November 2006 (UTC)

High temperatures and pressures are obtained in explosions - a nuclear explosion would probably be the best. That may not be useful. Alternatively for high pressure you could try Diamond anvil cell. For high temperatures you could try "electron beam furnaces" see http://www.theodoregray.com/PeriodicTable/Stories/077.x3/ . I don't know if these are the hottest but it's a good place to start. oxy-acetylene torches also get hot - about 3500 c according to wikipedia.

Experimental fusion plants are contenders for both highest temperature and pressure. You should also consider trying to find out what temperature the movement of the accelerated particles in particle accelerators is equivalent of, as temperature basically just is "average movement of molecules" and particles in a particle accelerator reach incredibly high speeds. TERdON 03:30, 18 November 2006 (UTC)

So light is the hottest thing in the universe? :) Or maybe tachyons, they are even faster (if they do exist). --V. Szabolcs 20:38, 18 November 2006 (UTC)

Known black holes

What is the number of known black holes in the universe?

I don't personally understand astronomy very well, but after a Google search, it seems that there have been 300 identified sources of gamma rays, which black holes are believed to spew out. 100 of these black holes are are the "brightest supermassive" ones of the bunch, found in other galaxies. It's believed that there are millions of black holes, but this gamma ray detection observatory has found 300. [[13]] -Chickenflicker 04:15, 18 November 2006 (UTC)

Depends what you mean by "known". We don't really know any black holes exist, because general relativity could break down under those conditions. —Keenan Pepper 05:18, 18 November 2006 (UTC)

There's a lot more than three hundred. Pretty much every quasar/blazar out there is presumed to be driven by a supermassive black hole - I have no idea what the current catalogue is, but it's fairly large. Galaxies without AGN can still have supermassive black holes at the center, as well (such as ours), and there's lots of those. And then there's all the smaller black holes that can be found in a single galaxy - I think there have been a few "directly" observed in the past year or two, but I forget when/where. But as far as absolute confirmation of what we think is a black hole, Keenan has a point. All we can really see is the effect of something really massive that's compact and doesn't emit light (aside from jets/accretion disks). Virog^{It's not}_{my fault!} 08:04, 18 November 2006 (UTC)

Number of body cells

What is the total number of body cells?

"[H]umans have an estimated 100 trillion or 10¹⁴ cells." See Cell (biology). Why is there a blue dotted line box around my text? 68.112.172.251 04:02, 18 November 2006 (UTC) (Chickenflicker, not logged in)

Cause you have a leading space. --Wirbelwindヴィルヴェルヴィント (talk) 04:08, 18 November 2006 (UTC)

Many thanks. Chickenflicker---♣ 04:24, 18 November 2006 (UTC)

Well, that's a very rough estimate. According to [14], some sources estimate the number of cells as 10 trillion. So I think the actual number is somewhere between 10 and 100 trillion cells. --Bowlhover 04:04, 18 November 2006 (UTC)

That's a pretty rough estimate as well, haha. Chickenflicker 04:05, 18 November 2006 (UTC)

Yup, these kinds of things are very difficult to estimate. You can't just take a human, take a microscope, and start counting the cells. --Bowlhover 05:45, 18 November 2006 (UTC)

Since everyone has a different sized body there is a lot of variation. But how hard could it be to get an estimate of the number of cells in a body - surely if you know the size of all the different tissues and the number of certain cells per amount of volume you can calculate it. I didn't word that last sentence well but ah well --WikiSlasher 12:08, 18 November 2006 (UTC)

Funny, I asked myself this question just yesterday and made a quick calculation. Assume one cell is 1 mm across and a human has a volume of 1 m³, then there are 1000³ = 1 billion cells. The human body is somewhat smaller, but cells are a whole lot smaller, so I guessed the number would have to be several orders of magnitude greater. However, the cell (biology) article says there are about 100 billion cells, considerably more than I guessed. The average cell must be less than 0.1 mm across.

Btw, the reason I asked myself this is that I wanted to have an idea of which lifeforms constituted the most cells on Earth. Form the numbers in the species article one may conclude that there are several times more species of bacteria than all other lifeforms put together. And given their size, there are probably more individuals per species than for bigger species, so they probably outnumber the rest in that respect too (anyone know this?). But what about biomass? So I decided to look at the number of cells. Assuming there are 5 billion humans with 100 trillion cells then together they have 5 × 10²³ cells. The bacteria article says "The number of Bacteria in the world is estimated to be around five million trillion trillion, or 5 × 10³⁰. So bacteria constitute a 10 million times more cells than humans. And how many cells do the other species constitute? There are only a few million species, so the bacteria still win easily. And that's not even taking into consideration that humans are a rather big and numerous species. Before I assumed that the one would compensate for the other, but humans are much more numerous than one would expect for our size. So I must conclude that this world still belong to the bacteria. All other lifeforms put together are vastly outnumbered in all respects. Sorry about the elaboration. Just having some fun with myself. :) DirkvdM 13:57, 18 November 2006 (UTC)

Even within the human body, bacterial cells far outnumber human cells (by number, but not by volume). Just something to think about. Tuckerekcut 16:33, 18 November 2006 (UTC)

Indeed, one millimeter is far too large for a cell’s diameter—if that were so, individual cells would be visible to the naked eye, and with a magnifying glass, you’d be able to make out organelles. The ovum is the largest human cell and is probably about 0.1 mm across, but I’d say the average human cell is probably only about 0.01 mm in diameter. But yes, bacteria easily win. — Knowledge Seeker দ 20:28, 18 November 2006 (UTC)

Fish bones?

Why do some fishes have many very tiny bones while others have only a few large bones? Is there an evolutionary theory that explains the fish bones? -- Toytoy 03:31, 18 November 2006 (UTC)

The most obvious explanation is that small fish have small bones and large fish have large bones. StuRat 04:32, 18 November 2006 (UTC)

If small fish had large bones, they wouldnt be able to fit them all in. And if large fish had only small bones, they would be too floppy. 8-)--Light current 17:27, 18 November 2006 (UTC)

Its all a matter of fish scale 8-)--Light current 17:28, 18 November 2006 (UTC)

And different types of bones often serve different purposes. --24.147.86.187 05:35, 18 November 2006 (UTC)

Differing evolutionary lineages.
B00P 08:59, 18 November 2006 (UTC)

As I know those little "bones" are not bones at all. (they are from some other material the bones are from) However, I don't know why some species have none of them and have only the vertebral column. --V. Szabolcs 20:31, 18 November 2006 (UTC)

Capacitance problem

This is another one of those "find the equivalent capacitance" problems that are common among physics students' homework. However this one is slightly different as it cannot be immediately reduced by the rules for series and parallel capacitors. The circuit consists of four junctions, a through d arranged in a square, such that:

1. The potential difference is applied across a and b, which are at opposite vertices.
2. Capacitors are connected between a and c, b and d, and c and d.
3. Wires link ad and bc.
4. There are no other connections.

Google and the relevant Wikipedia articles aren't very helpful. Please show me how to reduce this circuit into something I can easily deal with using the formulae for series and parallel capacitors. Thanks. MER-C 09:17, 18 November 2006 (UTC)

Interesting - assuming the wires have negliable resistance then the voltage difference across bc and ad should be zero, therefore the voltage across cd is the full potential difference. Therefore if a is at +v, b at -v, then c is at -v, d at +v. This gives the voltage across db = 2v ie the full potential difference. The same applies for the capacitor ac. The result is all three capacitors see the same voltage - this is the same as having capacitors in parallel. so the total capacitance is the sum of there capacitances. (Somebody please check this to be correct)

I concur, I got 3 capacitors in parallel with some voltage source.

Power Voltages

Why are the Voltages in 50 Hz. AC system always a multiple of number 11 (eleven) such as 220kV, 132kV, 66kV, 33kV, 11kV etc.. Adilmohiuddin 10:00, 18 November 2006 (UTC)Adil

Also 475 kv, 440V etc. I asked this question a few months ago. I dont think I got an answer! 8-(--Light current 17:23, 18 November 2006 (UTC)

Are you certain that they are at the first place? Here in Sweden, we switched a couple of years ago from 220 volts for household use to 230 volts, as I understand the latter is the European standard.... \Mike(z) 19:43, 18 November 2006 (UTC)

Yeah were not talking LV really. More like distribution voltage levels 8-)--Light current 20:03, 18 November 2006 (UTC)

Sunlenses

Do suncontact-lenses (as in sunglasses) exist? Do they have them in 1 way mirror style? If not why? Keria 10:01, 18 November 2006 (UTC)

That would look cool. :) In Gangs of New York there is this guy with a glass eye with a bald eagle etched on it. At one point he even taps it with a knife ('ting ting'). I assume the actor was wearing 'lenses'. Sun-contact lenses make sense to me. One reason they might be difficult (ie expensive) to make is that you can't make them from just any material - it has to be easy on the eyes (literally). And the mirror version might look really freaky, so low sales, so again high price, I assume. DirkvdM 14:14, 18 November 2006 (UTC)

You can do all sorts of things with contacts now. Look at this, for example. Yeek! --jpgordon^∇∆∇∆ 15:20, 18 November 2006 (UTC)

I don't think they would be safe. Those with a fixed level of shading would be dangerous because you would be blind when you went into a low light area and you can't just take contacts off quickly like you can with sunglasses. Photosensitive lenses, which darken when the light level goes up, are a possibility. However, the sunglasses I've seen that do this react too slowly. So, while driving, if you caught the glare from the Sun's reflection off a windshield, you would then be completely blind for several seconds after the glare ended, until the contact lenses returned to their lower shading level. In those seconds, you may very well get into a serious accident.

Perhaps there would be a few cases, with a universally high illumination level, where shaded contacts might make sense. Skiing comes to mind, but shaded ski goggles could also protect the eyes from snow, ice, and cold, dry air. StuRat 22:13, 18 November 2006 (UTC)

Do animals have the period?

I have never seen a bloodened dog due to that. Thanks.

They may do, but animals generally mate when they are in season. Dogs only come into season twice a year (and Dingos once), so it would be very uncommon for them to have a period if they had one, and it would probably be too small to see it. --liquidGhoul 13:58, 18 November 2006 (UTC)

Hmm, this is a bit of a girlie thing and here is another guy answering, but I believe only pregnancy will prevent menstruation. Just mating won't help. Period. DirkvdM 14:20, 18 November 2006 (UTC)

Oh, and ever noticed how dogs lick their behinds? This might be one reason. Funny this comes up. I'll be having black pudding for dinner in an hour or two. Yummy! DirkvdM 14:21, 18 November 2006 (UTC)

the difference here is menstruation, ("having a period") vs. oestrus ("going into heat"). Humans, some other primates, bats, and shrews menstruate; other animals, including dogs, have estrous cycles. Details, including some specific to dogs, are covered in the latter article. - Nunh-huh 14:50, 18 November 2006 (UTC)

Friend of mine had some bitches once. He said thay used to bleed over the carpet. 8-(. Could be to do with whether they had been spayed or not. --Light current 15:57, 18 November 2006 (UTC)

I remember seeing a National Geographic documentary, where they visited the zoo in Antwerp,Flanders. The female people who worked with the monkeys had noticed that after a while, their own periods became synchronized with those of the female monkeys! Can you believe that?!Evilbu 16:10, 18 November 2006 (UTC)

Yes. Pheromones ?--Light current 17:11, 18 November 2006 (UTC)

I believe cats and dogs don't experience periods unless they live with humans. There are diapers for them designed for their periods, but they're usually not in great amounts. I believe it was also "Consequences of a long-term raw food diet on body weight and menstruation" that talks about women who eat a strict diet will also be rid of their menstuation cycles, such as a wild cat or wild dog would. --Wirbelwindヴィルヴェルヴィント (talk) 17:37, 18 November 2006 (UTC)

For example, see Menstuation - Is it Really Necessary or google search for "menstruation diet human unnatural raw". --Wirbelwindヴィルヴェルヴィント (talk) 17:41, 18 November 2006 (UTC)

For the actual facts, please consult the articles I mentioned above, especially estrous cycle. Neither dogs nor cats menstruate. Some dogs or cats may have occational bloody vaginal discharges, but not all do, and they are not equivalent to menstruation. - Nunh-huh 17:45, 18 November 2006 (UTC)

Data Tables

Hi, I'm doing a science fair project. And I need to make a data table, but I need some help. Could you make an example. It is a project about ants and what foods they like to eat. The different foods are sweets,carbohydrates,water,and proteins. Water is the control and the food are the variables. What would be the depent variables? What can of data table would I use? How I make the data table. Any suggestions on how to improve the project? Thank a lot. - Mrs. Lellek

Oh, Mrs. Lellek, how many years have you been married? Try reading line chart, dependent variable, and independent variable. X [Mac Davis] (DESK|How's my driving?) 21:27, 18 November 2006 (UTC)

How about something like this:

FOOD
CONSUMED
PER
ANT
(mg)
 ^                      # SWEETS 
 |             #
 |        #
 |     #                o CARBS
 |   #        o
 |  #   o
 | # o 
 |#o 
 |o@@@@@@@@@@@@@@@@@@@@@@ PROTEIN
 +----------------------->
  WATER SUPPLIED PER ANT (ml)

Of course, I just made up the graph, your actual data would need to be filled in. StuRat 21:56, 18 November 2006 (UTC)

Gemstones

Can all minerals be gemstones. Explain. Thanks.

with a few exceptions - yes -pretty much so - even the lowliest piece of ground dirt if properly cut and polished can become a gemstone. Common minerals such as granite or feldspar can look nice. However some minerals are just too soft to be cut a polished - eg talc, clay, possibly mica and rock salt. Sedementary rocks present a problem becauce they are friable - however if you must mount for instance sandstone - it could be cut to shape and then coated in clear resin or varnish to give it a hard flat surface. A gemstone is just a stone that has be prepared for jewelry type use.. — Preceding unsigned comment added by 87.102.12.158 (talk • contribs)

Colo(u)r codes in molecular images

In images of (organic) molecules there seem to be customary to use certain colors for different kinds of atoms, for example carbon in black, sulfur in yellow and nitrogen in blue. How come they got these colors? I mean, the colors of carbon, sulphur or chlorine atoms may be reasonable from the elements' physical properties, but I've always wondered why nitrogen is considered to be blue, oxygen red (fire?) or phosphorous purple. \Mike(z) 19:37, 18 November 2006 (UTC)

• I have some guesses: oxygen, I think, has become red because of its association with oxygenated hemoglobin, and elemental nitrogen emits blues light when it ionizes (ever wonder why our 80% nitrogen sky is blue, but only in the daytime?). Hope that helps. – ClockworkSoul 19:42, 18 November 2006 (UTC)

There's no standard - sometimes hydrogen is red and oxygen white. As for nitrogen - "why not?" seems the most polite answer - don't expect any consistent reasoning for representational colours..

Plus after red, white and black for C, O and H whats left for N- blue or green would be common choices - it's like lego.

So what you're saying is: it's purely a coincidence that in most (virtually all) images I've seen on en:wp the system of oxygen <-> red, nitrogen <-> blue, hydrogen <-> white (or light gray) - identical to what I've been accustomed to from school - is used? And ok, I didn't know there are different conventions for oxygen/hydrogen, so if there are other atoms which by different authors/image makers get different colors, I'm happy that there (usually) are text descriptions of the molecules shown in the articles, so that any wp reader used to another color convention than is used here won't get confused by two too similar depictions as of e.g. thioesters versus thionoesters (only difference according to the wp article is that oxygen and sulfur switch places). \Mike(z) 22:47, 18 November 2006 (UTC)

Edit: While writing, I did a quick check on commons and saw there a number of instances where the creator used a blueish green for carbon - those creators doing so whom I did check seemed to come from Germany or the Netherlands, so there is perhaps different customs in different countries. But ok, it seems as nobody will be able to point me to the article describing the "history of images depicting molecules" :)

Safety question

Is it safe to grind saltpetre (potassium nitrate) in a coffee grinder?

on its own - yes.

Though I should say, that if you don't know the answer to that question you shouldn't be working/messing about with it.

You should fill in a Risk Assessment form before proceeeding and take suitable precuations to minimise the risk of damage to health (both yours and other peoples) 8-)--Light current 20:26, 18 November 2006 (UTC)

Don't forget to read potassium nitrate and this link from that article gives a chemical substance safety description http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0184.htm

Not so safe if the next person grinds coffee in the same grinder! And be very careful not to combine your finely ground saltpeter with finely ground anything else. Edison 22:00, 18 November 2006 (UTC)

Well exactly! That should be covered in the Risk assessment! (harm to others) 8-)--Light current 22:04, 18 November 2006 (UTC)

Anabolic Steroids

I was wondering why when people use steroids, they stack them and not just use one thing? I thought just the steroid will raise testosterone levels, why isnt it all you need? thanks