Wikipedia:Reference desk/Archives/Science/2006 November 15

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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I see this software, even the newest version, is outdated.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Outdated how ?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Um, this may be out-of-date terminology for all I know, but I think "hydrogen carbonate" is H2CO3.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)

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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)