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

From Wikipedia, the free encyclopedia

< Wikipedia:Reference desk | Archives | Science

Science desk
< December 14	<< Nov \| December \| Jan >>	December 16 >

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

[edit] December 15

[edit] Coilgun

Where could I get a good capacitor(s) for a coilgun?--67.172.248.207 01:33, 15 December 2006 (UTC)

read the article on coilgunsBeckboyanch 05:39, 15 December 2006 (UTC)

The coilgun article doesn't directly answer your question, but it does link to a page describing a home-made coil gun, in which the constructor says he used "two capacitors that I pulled out of an old CRT monitor". Gandalf61 10:52, 15 December 2006 (UTC)

See also the PowerLabs - Coilguns page. ☢ Ҡi∊ff⌇↯ 11:01, 15 December 2006 (UTC)

Make sure to judge how much you know about electrical engineering and physics already. If you don't know where to get a capacitor for this, you might not be a good candidate for trying to build it, which is presumably what you are doing. Ebay always works, :) X [Mac Davis] (DESK|How's my driving?) 19:25, 16 December 2006 (UTC)

Ive heard that Maxwell make good high voltage capacitors. See ~~User:BillC~~ whoops it User:Bert Hickman page on coin shrinking. He uses BIG caps. You could also try Sphere Research [www.sphere.bc.ca] . They have all sorts of weird goodies!--Light current 20:16, 16 December 2006 (UTC)

[edit] "Sodium Coma"

While not looking for medical advice, I am curious to biochemical reason why I get extremely sleepy after eating lots of salty foods (olives, snack chips, processed cheese). It's like a dense sleepitime fog falls over me and I routinely fall asleep if I'm sitting down. I jokingly refer to as as a "sodium coma". It's a different feeling the typical post-Thanksgiving carb overload. --72.202.150.92 01:47, 15 December 2006 (UTC)

Hmm, could it be Vasopressin? --W o o ty Woot? contribs 02:00, 15 December 2006 (UTC)

Sleepiness from NaCl is not an expected response. Could it be that the foods contain Tryptophan, and that you are sensitive to this? The article has a list of foods rich in this amino acid; you may wish to compare that with your sleepy snacks experience. --Seejyb 15:09, 15 December 2006 (UTC)

Could it be something simple like you're not getting enough water Nil Einne 13:58, 21 December 2006 (UTC)

[edit] Herion OD = 1-10mg Narcan. Cocaine OD = ?

When treating a Heroin overdose, an injection of 1-10mg Narcan is given. This snaps them out of it - but Narcan only works for opiates.

What is used for stimulants such as cocaine or amphetamines?

--69.138.61.168 04:27, 15 December 2006 (UTC)

There is no equivalent "reversal" agent for cocaine or amphetamines. People who overdose on cocaine or amphetamines are treated symptomatically; they may be sedated; they will be treated for complications such as fever, convulsions, or heart attack if they occur. - Nunh-huh 04:36, 15 December 2006 (UTC)

Reference Desk is not a good source for medical advice. Please contact a doctor or other valid source. Edison 15:23, 15 December 2006 (UTC)

No medical advice was asked for, and none was given. Please take note of what "medical advice" actually is, and please stop leaving messages suggesting it was given when it wasn't. - Nunh-huh 04:29, 16 December 2006 (UTC)

However, to pique your interest in the science of pharmacology: Yes, there is no specific receptor antagonist to those drugs, so one is left with the supportive therapy (no article yet, but in principle a more drastic form of symptomatic treatment) that Nunh-huh describes. The other specific antagonist you may hear about is flumazenil, which antagonises a benzodiazepine coma (for which naloxone won't work). --Seejyb 15:39, 15 December 2006 (UTC)

[edit] Steroids and HGH

Would it be correct to say steroids cause the expansion of muscle fibers and Growth Hormone causes an increase in the number of muscle fibers?

Anabolic steroids can increase muscle mass, but can cause "elevated cholesterol (increase in LDL, decreased HDL levels), acne, elevated blood pressure, hepatotoxicity, and alterations in left ventricle morphology." Growth hormone increases the number of muscle cells in Danio fish but not in Zebra fish (I am in a rush, so cannot find the ref now, but will look later). Humans are like Zebra fish, so taking growth hormone to develop muscles is a waste of time. --Seejyb 16:38, 15 December 2006 (UTC)

OK, see P. R. Biga and F. W. Goetz. Zebrafish and giant danio as models for muscle growth: determinate vs. indeterminate growth as determined by morphometric analysis. Am J Physiol Regulatory Integrative Comp Physiol, Nov 2006; 291: R1327 - R1337. --Seejyb 22:02, 15 December 2006 (UTC)

[edit] Falling

What creates the sensation of falling one sometimes experiences just before sleep? Thanks! S.dedalus 04:58, 15 December 2006 (UTC)

For various theories, see hypnagogic jerk - Nunh-huh 05:04, 15 December 2006 (UTC)

Sleep paralysis? During sleep, the body is paralyzed to prevent the dreamer from acting out his dream. Sometimes, the body is paralyzed too soon, when it is still awake. Hallucinogens can occur for the same reason dreams occur, and of course, nobody can be certain why dreams occur. --Bowlhover 05:07, 15 December 2006 (UTC)

[edit] starfish

i have a dried starfish (bought at a tourist shop) missing parts of two limbs. is it possible to recuscitate it by placing it in salty water? Flowerykewlstuffz123 05:26, 15 December 2006 (UTC)

No. It's dead. It is an ex-starfish. - Nunh-huh 05:39, 15 December 2006 (UTC)

Sea star mentions that a starfish may regenerate from as few as a single ray, but as Nunh-huh mentioned above, the starfish you describe is pining for the fjords. - CHAIRBOY (☎) 05:42, 15 December 2006 (UTC)

'E's not pinin'! 'E's passed on! This starfish is no more! He has ceased to be! 'E's expired and gone to meet 'is maker! 'E's a stiff! Bereft of life, 'e rests in peace! If you hadn't shellacked 'im to the diorama 'e'd be pushing up the daisies! 'Is metabolic processes are now 'istory! 'E's kicked the bucket, 'e's shuffled off 'is mortal coil, run down the curtain and joined the bleedin' choir invisibile!! - Nunh-huh 05:46, 15 December 2006 (UTC)

"...and I never wanted to work in a fish store anyway, I always wanted to be a lumberjack...". StuRat 22:25, 15 December 2006 (UTC)

Just in case anyone does not understand the allusion - see Dead Parrot. And a stiff is just a corpse. There are no hidden meanings here. Gandalf61 10:44, 15 December 2006 (UTC)

At least, there weren't, until you alluded to them. :-) —Ilmari Karonen (talk) 13:22, 16 December 2006 (UTC)

While some animals can survive dehydration, a starfish is not one of them. I tried once, and got a soggy, dead, starfish. (It didn't smell nearly as pleasant as you might imagine.) StuRat 22:25, 15 December 2006 (UTC)

If you take the starfish, place it in 700 ml of water at hand temperature, cover with a lid, and microwave for about 4 minutes on maximum power, it may be woken up by the sudden blast of warmth combined with microwave energy, and this can trigger its rejuvenation.

Of course, there is the other 99.3% of a chance that you'll end up with a really impressive explosive superheated mush coating your microwave's interior, but thats just the risk you have to take if you want to revive such creatures from their descent into the abyss. FT2 ^{(Talk | email)} 01:00, 17 December 2006 (UTC)

[edit] Hallucinogens in palliative care?

Have hallucinogens ever been used or proposed for palliative care? It seems to me that they could, at least in theory, do three things to help a terminally ill patient who is no longer capable of communicating with others (whether due to blindness and deafness, loss of speech, diminished mental functioning or just institutionalization without access to loved ones): relieve boredom, decrease awareness of physical distress, and provide spiritual experiences that might help reconcile them to their upcoming death. Neon Merlin 06:13, 15 December 2006 (UTC)

According to this article, yes. However I would think that administering any non-medically-necessary substances to someone incapable of indicating consent would be illegal, or at least severely unethical. Anchoress 06:29, 15 December 2006 (UTC)

Well then, suppose the patient had given consent in advance? Neon Merlin 12:48, 15 December 2006 (UTC)

Hmmm... I don't know. I suppose somebody who has information on the legal constraints surrounding drug administration might know. Anchoress 12:55, 15 December 2006 (UTC)

Bad trip + can't communicate = bad idea. --W o o ty Woot? contribs 10:42, 15 December 2006 (UTC)

Yes, they have been proposed and used for palliative care. This BBC reportgives an overview of possible uses. Note that this use does not refer to persons who cannot communicate, but that any therapy is guided by the patients' reports of an improvement of quality of life. Another way of thinking about this: 1. When a person cannot communicate, then only medical signs can be treated (not symptoms, since these rely on reporting). 2. Signs can usually be managed by "conventional" medications. 3. Is there such a sign as "lack of hallucinations"? --Seejyb 16:17, 15 December 2006 (UTC)

I don't have much in the way of sources... try erowid's vault which has huge archives on psychoactive drugs and their research. But yes, in the period between discovery of psychoactive drugs such as LSD, and their banning by the US Government, they were extensively tested for use in therapy, palliative care, and many other situations. FT2 ^{(Talk | email)} 00:56, 17 December 2006 (UTC)

[edit] Repetition speed for strength exercises- fast or slow

Hi there,

Could someone tell me what are the pros and cons to different repetition speeds when doing weight exercises?

Best regards,

Amsbam

I have only anecdotal information (that which I've gleaned from various fitness instructors), such as that fast reps are to be undertaken with caution because it increases the likelihood of injury; slow reps are better because they work the muscle better, etc. But I have no references for those assertions. You might want to look at some of these links, which seem to have more info. Good luck, and maybe someone with more information/education will chime in. Anchoress 08:55, 15 December 2006 (UTC)

Appreciate the insight Anchoress, thanks.

[edit] Withdrawal of Supplies of amitripyline tablets

Here in the Seville area it is impossible to obtain amitriptyline tablets at present, since the begining of December. The story is that the pharmacists don't know why the supplies have stopped. They say possibly a change of tablet or change of package. In my experience, decades as a nurse, this is unprecedented. Has it happened elsewhere? Does anybody know what the real reason is? Thanks in anticipation

(Assuming you are not from Spain, but from Ohio) The information on shortages, kept by the FDA, can be found here, but amitriptyline is not mentioned. I assume you would then have to look for a local problem. Another ref desk editor may have local knowledge. --Seejyb 16:03, 15 December 2006 (UTC)

That type of supply disruption is not unique to medications (but may be a far more serious issue there) and is often caused by having a single supplier system. Another risk is usage of the just in time delivery system, where stocks are intentionally kept low to reduce storage costs. With the combination of the two, virtually any production or distribution problem can cause severe shortages. StuRat 22:16, 15 December 2006 (UTC)

OK, thanks for that.

You're welcome. I also looked at the FDA site on drug shortages: [1], but they don't list any shortage of amitripyline. I couldn't find any mention of a general shortage in Spain, either. StuRat 05:12, 16 December 2006 (UTC)

Thanks again for looking StuRat. Richard A.

[edit] earth

How old is the Earth 59.93.61.66 10:23, 15 December 2006 (UTC)

Age of the earth. Anchoress 11:07, 15 December 2006 (UTC)

[edit] Audio - Centre Channel Extractor on Adobe Audition

I suppose this should be a computer/software question but it mainly involves science so: How is it possible that one can isolate the "centre" channel of a stereo audio track? I understand how it's possible to remove the "centre" channel using one inverted channel combined with the non-inverted other channel. To use an equation: LC (left, centre) + -RC (minus right, minus centre) = L-R - thus removing the centre channel. It's impossible to remove the centre channel using this method, so how does a piece of software do it?

Not sure how this jibes with your equations, but a speaker connected from left channel phase to right channel phase, neglecting the ground connection of each channel, might extract the center channel (or maybe it completely suppressed the center channel!). Dolby prologic does fancier combinations; that's just a 1970's trick. Not sure how your Adobe Audition would correspond, since that trick was physical wiring. Edison 15:28, 15 December 2006 (UTC)

This would completely cancel the centre channel - which is very easy and simple maths. I'm talking about actually isolating the centre channel, disregarding the left and right (side) channels. Adobe Audition can do this. I don't know how though. I'm sure it's probably a closely guarded secret by Adobe, but would be interested to know if anyone has any theories. Out of phase separation (oops) is a very simple equation and process based on analogue waveform manipulation, Adobe's "centre channel extractor" must be very complicated and purely digital. Any thoughts?

I'm no sound engineer, but it seems that once you've cancelled the centre channel (left plus inverted right), you could just "subtract" what's left from the original signal in the same way (original plus inverted (left plus inverted right)) to get only the thing you cancelled, i.e. the centre. Maelin (Talk | Contribs) 02:19, 19 December 2006 (UTC)

No because:

(LeftCentre) + Minus(RightCentre) = (LeftMinusRight) (cancelling the centre channel)

Your proposal is to take that result and subtract it from the original to get pure centre channel, but what happens is:

(LC) + (-RC) = (L-R)

(L-R) + -(LRCC) = (-L+R-CC)

End result: Same as original source but with one inverted side channel.

I don't know about all your plus and minus stuff, but I do know that if you can eliminate the center channel, you can also isolate it. There may be an easier method, but what I do is 1:eliminate the center channel 2:mix both the new and the original signals into mono (that is, into two mono signals, one with the center and one without it), panning one completely left and one completely right. In that new mix, sound that had previously been in either the left or right channel(but not both) in the stereo mix is now equally in both left and right channels. The sounds from the original mix that were in the "center" channel are now off to one side. 3: Now eliminate the new "center" channel, the original center will be all that remains. Here is a little diagram to help explain my ramblings. I have used the letters A B and C to represent different sounds.

                    Left     Right       Left  Center  Right             Step 1           Left    Right
       original:     AC       BC     =     A     C       B       Remove Center Channel:    A        B
 
       Step 2       Left     Right       Left  Center  Right             Step 3           Left    Right
    pan signals:  ABC(or.)   AB(new) =     C     AB              Remove Center Channel:    C

[edit] ants

Are there any ants that specialize in eating termites? 71.100.6.152 17:31, 15 December 2006 (UTC)

I'm not sure you could regard them are specialists but carpentar ants will eat termites. http://ohioline.osu.edu/hyg-fact/2000/2063.html David D. (Talk) 17:43, 15 December 2006 (UTC)

Don't guess carpenter ants do as much damage as termites but I'm looking for an ant type that is small enough to chase down termites inside the tunnels they make in wood. 71.100.6.152 19:46, 15 December 2006 (UTC)

An insect inspector told me the Carpenter Ants dig out a hole in the wood to make their nest. Termites actually EAT the wood. So yeah, termites are more destructive. 12.10.127.58 21:10, 15 December 2006 (UTC)

To expand, carpenter ants do not destroy 'good' wood, termites do (that is the EAT bit). If you have a problem with carpenter ants then you have rotten wood, which is a problem without the aggrevation of the ants. David D. (Talk) 21:42, 15 December 2006 (UTC)

So seeing carpenter ants means rotten wood. Humm.. I'l put that away for future reference. 71.100.6.152 21:51, 15 December 2006 (UTC)

[edit] circumcision and aids

Do you folks really believe that circumcision helps us against HIV infections (see Circumcision#HIV) or it will just put circumcised men at risk?

It's in all the newspapers at present. http://news.google.com/news?client=safari&rls=en&q=circumcision%20AIDS&ie=UTF-8&oe=UTF-8&sa=N&tab=wn

Read the articles and see what you think. These types of reports are always open to interpretation. Primarily it depends on how many people were involved in the study. David D. (Talk) 17:46, 15 December 2006 (UTC)

Well, to be honest, does it matter? The risk will be there anyway, it's not like "ohhh, I'm circumcided, now I go do unprotected sex with strangers because I'm invulnerable to aids." Good sex habits cuts the risk by 99% 212.10.217.122 21:28, 15 December 2006 (UTC)

for the record, out of every 10,000 (ten thousand) people that have sex, only 5 people get an HIV transmission. There are far more dangerous things than sex, unless of course you're so horny that you have sex every day.—Preceding unsigned comment added by 70.225.160.106 (talk • contribs)

For clarity, the following factual answer uses correct medical terminology in an appropriate and responsible sense. Please do not delete this answer just because you are offended by this terminology or the acts that it describes. To be clear about the statistics in the previous answer, the average rate of HIV infection for unprotected penile-vaginal intercourse where one partner has HIV is indeed 5 in 10,000 acts for the male ("insertive") partner. However, the infection rate is 10 in 10,000 acts for the female ("receptive") partner in penile-vaginal intercourse, and it is 50 in 10,000 acts for for the receptive partner in anal intercourse - see HIV#Transmission and AIDS#Transmission and prevention. Also, note that these are average figures. Infectivity varies over a wide range according to the progress of the illness in the infected partner, and the presence of other sexually transmitted infections greatly increase the rate of HIV transmission. So the risk of infection from a single unprotected sexual act with an infected partner may be much higher than these average figures. There is indeed some evidence that circumcision reduces the infection rate for the insertive partner. However, a far more effective way to protect both partners from the sexual transmission of HIV and other STIs is to correctly use a condom. Gandalf61 09:54, 16 December 2006 (UTC)

Understand that condoms have a finite effectiveness. Condoms can break at rates as low as 90-95%. So what that means is that receptive anal sex with a condom is about as risky as insertive fellatio. Regular sex with a condom 10 times (many people do that in a week easy) is as risky as insertive fellatio. —The preceding unsigned comment was added by 70.225.160.106 (talk) 16:21, 16 December 2006 (UTC).

I believe the above comment was meant to say "condoms break at rates as high as 5-10%", right? --18.214.1.72 23:28, 16 December 2006 (UTC)

Any statistics can only be a guide, and often not a very acurate one. For example, here are some confounds (unplanned-for factors which influence or confuse results):

What type of "condom" are we going to use. there's no "average" condom, a specific person usually has one consistent choice - thin, ribbed, normal, strong, length, tightness, age, manufacturer, storage conditions, lubricant used
What kind of sex and how do you do it - vaginal, oral, anal, long duration, brief, shallow thrusts, deep thrusts, fast, slow. Again, these are often quite consistent person to person.
How aware and careful are you about your condom use - before sex, how it is on the penis during sex, and its removal after sex. Likewise consistent.

So the problem is, that Jim has regular vaginal sex, he habitually uses a strong condom, his girlfriend likes it gentle, and he orgasms after 2 minutes in which time the condom stays where it was put. Andrew has anal sex and likes it rough, he's buys the ordinary condoms his local store sells.... their risks for each act will be very different, and that's consistent. Lessons:

Be very wary of applying generalized statistics to one situation where the situation may consistently not match the basis of the statistics
Think about safe sex in the context of your love life, not some other persons.

FT2 ^{(Talk | email)} 00:52, 17 December 2006 (UTC)

[edit] phosphoric acid as electrolyte

I recently left some copper on one side and some iron on the other side of a dish full of 30% phophoric acid and bubbles started coming from both metals and the iron began to take on a copper color. Does this mean that any acid will cause self-plating without an external current being supplied or does this only happen in phosphoric acid or is this really self-plating at all? 71.100.6.152 18:34, 15 December 2006 (UTC)

There could have been some copper oxide on the copper that would react with the acid forming a copper compound - this would then plate the iron in the same way a copper sulphate solution does. Question - after a while was the copper clean (ie pink) - if you add more iron does it continue to plate with copper - I'm guessing that your mixture will only have a limited copper plating capacity.87.102.8.6 20:24, 15 December 2006 (UTC)

Also copper phosphate is usually insolouble in water - which makes me slightly suprised you got any copper plating at all.. The same goes for Iron phosphate as far as I know - I would have expected to get a layer of metal phosphate on the surface of each metal and not much more - just goes to show how experiments are more valuble than theories.87.102.8.6 20:38, 15 December 2006 (UTC)

Checking again after an hour revealed that the release of bubbles had slowed way down. Only the bottom portion of the iron up to the level of the top of the copper seems to be plated. The color is somewhat pink and flat. Above this the iron is turning black whereas when it was in the acid before the copper was added it was flat gray. I'm wondering if the acid is separated into copper phosphate and iron phosphate such that the layer surrounding the pink area is the copper phosphate while the area above is the layer of iron phosphate. The copper is somewhat dark but not black or real dark. 71.100.6.152 21:46, 15 December 2006 (UTC)

What color is Iron Phosphate? If it is reddish, then it may imitate the color of copper as the Iron begins to react with the phosporic acid, leaving a residue 'plated' to the Iron surface. 12.10.127.58 21:10, 15 December 2006

(UTC)

Both layers of acid are clear. The "plating" on the iron is not redish but black. 71.100.6.152 21:46, 15 December 2006 (UTC)

Iron phosphate will probably be very dark - eg black see http://www.ilve.com.tr/en/surface-treatment/index.html or even better Parkerizing - if the iron is black now it's almost certain that the surface is iron phosphate - (what I would expect)

'pink and flat' as you describe it is how copper usually looks when it's initially plated - take it out of the liquid and it will slowly change to more common red copper colour as it oxidises in air.87.102.3.159 22:29, 15 December 2006 (UTC) Can you expand on " Only the bottom portion of the iron up to the level of the top of the copper seems to be plated" - these seems to me to mean that some of the iron has gone black and some pink.. All the iron is submerged in the acid? and the copper is not touching it?

Check now after about 3 hours hear is what I see...

71.100.6.152 23:27, 15 December 2006 (UTC)

has the acid got any colour now (copper phosphate probably blue or green) - it is possible that any dissolved salt eg Copper phosphate would settle towards the bottom in a still liquid. By the way the bubbles may not neccessarily by hydrogen - but may be simply dissolved air coming out of the liquid on the metal - this is not unlikely.87.102.8.141 22:09, 15 December 2006 (UTC)

The clear acid is now slightly green. 71.100.6.152 23:29, 15 December 2006 (UTC)

The green colour is almost certainly a dissolved copper compound (though to complicate things some iron compounds are also green).

Looks like any dissolved copper has stayed at the bottom - this isn't unrealistic as long as you don't stir the liquid. Is the black layer transparent ie clear or is it a precipitate ie made of suspended solid? (Also did you mix the acid with water - sometimes you could get a layer of water sitting on top of a layer of acid.)

From your diagram it looks like some copper has dissolved and diffused along the bottom plating the iron as expected. I'm a bit confused about the black layer as I wouldn't expect it to float to the top. Clearly coating the iron with copper prevents the competing reaction which is formation of iron phosphate. I'd guess no more bubbles have been formed? It sounds like what is happening is slow corrosion of both metals in acid with some competing chemical plating (this is electroless plating). As a suggestion I'd suggest adding another bit of iron just to see if it reacts in the same way. Also you could (if you have a pipette or similar) remove some of the liquid from the top, middle and bottom layers and see what effect that has on a new iron piece in three separate bottles..

As to your original question - this is electroless plating - usually to electrolessly plate with copper you would need a copper salt eg copper sulphate, is this case though it looks like the copper salt is beeing made 'in situ' by reaction of the copper with the acid. This situation is restricted to phosphoric acid - it would happen with other acids as well; though copper is not very reactive and how much dissolves would depend on the acid used - nitric acid dissolves copper easily but sulphuric acid dissolves copper very slowly.87.102.3.159 23:57, 15 December 2006 (UTC)

If I stir up the acid a lot then the bubbles increase again. The dark layer at the top disperses somewhat in the acid and makes it a bit darker and cloudy. The copper now seems to be somewhat coated with a light layer of iron oxide, i.e., rust. Before taking a sample of each layer to test reactions with iron I have placed the iron in contact with the copper. This has slightly increased the bubbles from the iron but not by a whole lot. I’m curious if electroless plating done in this or a better way can be made sufficient enough to serve as a corrosion barrier for iron in air.71.100.6.152 01:22, 16 December 2006 (UTC)

I think in general electroless plating would be done with a already prepared solution of the metal to plate with, eg in a simple example you would place the iron in a copper sulphate solution - it's not really as good a method as electroplating - since once the iron is covered with a thin layer off copper no more is deposited - so only very thin coatings can be obtained - for a corrosion barrier electroplating, galvanising, or parkerizing would probably be preferable. The layer produced by electroless plating just isn't thick enough to give really good long term resistance to corrosion - though it is better than no coating at all.87.102.4.180 11:51, 16 December 2006 (UTC)

So then the difference between electroplating and electroless plating is not that in electroless plating all of the metal in the solution is used up which in an electroplating is replaced by the atoms in the anode but because the cathode (in this case) reaches electrical equilibrium as soon as it is covered with copper? 71.100.6.152 15:14, 16 December 2006 (UTC)

You've got the difference right, sort of, I not sure if my answers were clear enough..

Obviously you know what electroplating is and how it works.

In electroless plating the reaction stops not because of an equilibrium being reached (being pedantic), because there will still be iron under the copper to react and probably copper still in solution. The plating stops because all the iron surface will be covered with copper - the copper forms a barrier preventing any more iron reacting. Once the iron is all coated with copper it is effectively electrochemically 'insulated' from the solution.

Also with electroless plating some of the iron must dissolve to get copper coating - it's the reaction Fe_solid + Cu2+_solution >>> Fe2+_solution + Cu_solid, this means that the 'iron' must be more reactive than the copper, (so silver and gold plating also work). However in electroplating the iron does not need to react - since the reduction of the metal in solution is done 'electrically' - so Iron can be electroplated with metals that would not normally react eg Ni or Cr.

In electroplating the 'work' is done by the electricity, in electroless plating the work is provided by the iron dissolving. 87.102.4.180 16:15, 16 December 2006 (UTC)

Yes, that is what I was asking (although it appears that there is such a thing as Electroless nickel plating). This would explain how flaw in the iron might be "corroded" beyond and acceptable amount if electricity were not used to do the plating. In other situations it seems that electroless plating might actually be beneficial for this reason by helping to expose certain flaws at least using phosphoric acid. Would all acids cause iron to disolve or just phosphoric acid? 71.100.6.152 13:24, 17 December 2006 (UTC)

yes, that's right. answer - most acids will dissolve iron, including weak acids like vinegar (acetic acid), a few don't (concentrated nitric) becauase they 'pacify' the iron surface see http://www.cci.ethz.ch/experiments/Passivierung_Fe/en/stat.html. (Note I think electroless plating is sometimes used to coat iron/steel with copper prior to electroplating with chrome - a bit like a primer as used in paints).87.102.13.235 16:06, 17 December 2006 (UTC)

The iron wire now removed from the phosphoric acid shows copper plating where the bubbles rose to the surface as well. some parts of the wire remain black but other parts have already acquired a surface coating of rust. I'm now going to put some nickel in a clean batch of phosphric acid and then put in some iron after the nickel that is left is removed in hopes of doing the electroless nickel plating. 71.100.6.152 21:00, 17 December 2006 (UTC)

[edit] Gums

How do gums stick things together61.0.133.51 18:37, 15 December 2006 (UTC)

Could you be a little more specific - what kind of gum? Postage stamp gum, perhaps? If not, take a look under adhesive and gum, maybe it has the information you need? — QuantumEleven 20:16, 15 December 2006 (UTC)

[edit] The Temporal Resolution of the Compound Eye

Why is the temporal resolution of the compound eye higher than that of the human eye? Please don't tell me "The compound eye has a higher flicker fusion rate." because that is only a restatement. Which are the processes in which the compound eye / visual system is faster and why is it? Falk Lieder 18:52, 15 December 2006 (UTC)

See: Interference and Photoreceptor recovery rate opps... not yet an article. Try Photoreceptor#Advantages and Visual phototransduction instead. Adaptron 19:07, 15 December 2006 (UTC)

My understanding is that the answer would be found in the second link - if it existed:) In the compound eye the rhodopsin is a bistable molecule - on absorbing a photon it changes from metarhodopsin, the retinal changing to the all-trans form. On absorbing a second photon, the metarhodopsin changes back to rhodopsin. It is the first change that initiates depolarisation, via a G-protein coupled mechanism. The second reaction simply restores sensitivity, i.e. it does not cause any further depolarisation. This flip-flop of rhodopsin-metarhodopsin-rhodopsin occurs repeatedly, it is quick, it does not deplete the supply of rhodopsin, and explains the rapid response of the compound eye. In vertebrates, by contrast, rhodopsin undergoes "bleaching" - the retinal splits off from the opsin protein, and the rhodopsin now has to be regenerated by relatively slow enzymatic means. So the difference seems to lie in how quickly the rhodopsin at a specific site can be regenerated. If the regeneration / recovery time is short, then a higher frequency flicker can be detected, but if it is slow, then the sequential flickers fuse at slower rates. The difference between the two rhodopsins (compound eye and vertebrate eye) lies in the opsin, not in the retinal part of the molecule - all animals have essentially the same photosensitive retinal component. The opsins differs, and determine wavelength sensitivity, whether the metarhodopsin can be directly reactivated, or whether it bleaches and has to be resynthesised. I hope this helps, and please ask if my explanation is dense - unfortunately I do not have a reference with me. --Seejyb 01:34, 16 December 2006 (UTC)

Thank you very much for your excellent explanation! Falk Lieder 18:16, 16 December 2006 (UTC)

[edit] High temperature nuclear waste repository

Have any high temperature nuclear waste repositories been designed to concentrate the high temperature waste and use the heat to perform work such as boiling and thereby distilling water (through heat exchangers of course)? Adaptron 19:03, 15 December 2006 (UTC)

No. The risk of contaminating ground water is very high already. When cheap fossil fuels abound, why bother messing with dangerous toxic wastes to produce energy? 70.225.160.106 04:13, 16 December 2006 (UTC)

By putting nuclear waste to beneficial use the deliberate effort to eliminate it as a source of contamination would be greatly enhanced. Besides naturally occuring deposits Natural nuclear fission reactor of radioactive material have been found which at one time had critical mass and were shielded only by overlayment and groundwater. Adaptron 16:01, 16 December 2006 (UTC)

[edit] Digitising photos

More of an "advice" than a "knowledge" question, but I'm hoping you wizards of the reference desk will be able to help me nonetheless :). I have a large number (several hundreds) of photos printed from 35mm film, with their original negatives. I would like to digitise them if possible, with the aim of being able to print off the digitised versions (instead of having to take the negative into the photo shop to have the reprint made). I have experimented with the scanner at work, but the quality from scanning the photos in is not all that great (even after fiddling with the settings for awhile) - plus, for several hundred photos, it's not necessarily the best solution. Does anyone have ideas for digitising photos to "reprintable" quality? A film scanner, maybe? Thanks in advance for any tips! — QuantumEleven 20:13, 15 December 2006 (UTC)

Yeah, I would try a film (negative) scanner. Personally I have found them to be somewhat spotty, so you should really try to make sure you read reviews for them and possibly try out one yourself if you have the ability to. As for scanning the prints themselves, is the "scanner at work" an old mopier beast, or is it a relatively new flat-bed scanner? If it is not the former, that might be the source of your poor quality — you might want to try out a more up-to-date dedicated scanner. In my experience many old scanners and mopiers and things like that have far inferior quality to even a cheap flat-bed made in the last year or two. --140.247.240.127 20:55, 15 December 2006 (UTC)

I believe many places where you can develop film will now also give you a digital version on disk, for a price, of course. The advantage is, you only have to pay once, and can make all the copies you want after that. StuRat 22:08, 15 December 2006 (UTC)

most of them give you 1.5 MP images at a crappy JPEG quality. doing it yourself is better.

That would be suitable for e-mail, but your right, is grossly insufficient for "reprintable" quality. On the other hand, only the most expensive scanners would have any hope of reproducing a photograph without a noticeable loss of quality. StuRat 05:02, 16 December 2006 (UTC)

Get a scanner (Minolta, Nikon..) that's made for scanning film. many of them come with a tray that will feed uncut film rolls or 4-strips automatically, and software that will crop it properly and spit out a series of high-quality JPEGs or TIFFs.

Just a thought... would projecting the negatives on to a screen and taking the photographs using a digital camera help ? Of course, you'll need to convert the photos into their 'negatives' using some software on your PC to get the original colours. Besides, you'll also need a projector... --WikiCheng | Talk 10:25, 16 December 2006 (UTC)

It would be very hard to get the colors right in something like that (even more so if doing it from negatives). And most digital cameras are going to have far less resolution in the final file than you could get from a scanner. Better to scan directly. --24.147.86.187 15:47, 16 December 2006 (UTC)

There are a number of commercial services that will scan negatives for you, which can be cheaper and less time-consuming than scanning them on your own. Do a Google search for "negative scanner" and look at the sponsored links (ScanCafe looks pretty promising). howch e ng {chat} 18:37, 18 December 2006 (UTC)

[edit] Tobacco Addictiveness

Could somebody tell me the exact addictiveness of tobacco and it's addictiveness compared to other drugs? A link to where the info was aquired and/or a trustworthy source for this information would also be nice (somewhere other than Wikipedia). BeefJeaunt 20:28, 15 December 2006 (UTC)

How would you quantify "addictiveness" ? One way I could think of is as a percentage of people who are unable to quit. StuRat 22:04, 15 December 2006 (UTC)

Okay, forget "exact addictiveness". How addictive is tobacco compared to other common/well-known drugs, eg. cocaine, marijuana, alcohol, etc. I read here that nicotine "with a 90% addiction rate, is the most addictive of all drugs". I'm somewhat skeptical and would like to have this information verified (if at all possible). I also read that 70% of current smokers have tried to quit at NIDA's site, so I already have that statistic. I'm writing a thesis for grade 10, "Marijuana Vs. Tobacco", just in case anybody's suspicious.

I think this site will answer your question: [2] added by —AySz88 \^-^ to replace [3]. Check out the chart at the end, especially. They tested nicotine, heroin, cocaine, alcohol, caffeine, and marijuana, and found marijuana to be the least addictive, with an approximate tie with caffeine. StuRat 04:50, 16 December 2006 (UTC)

To avoid pre-disposing people to the findings of the article, I replaced the link above with a plain text version of the news article. (The original had a bunch of interpretations and highlighting to point people to one specific finding which isn't really relevent.) —AySz88 \^-^ 04:21, 18 December 2006 (UTC)

[edit] Conjunctivitus

I am NOT seeking medical advice here or anything, but I would like to know: what are the symptoms of conjunctivitus; and what are the cures and/or preventions? thanks Herbynator 22:28, 15 December 2006 (UTC)

Conjunctivitis explicitly states symptoms and treatments. Preventative measures you can take: avoid touching/rubbing/itching your eyes/face/nose as much as you can, scratch your face with your (upper) arm if you can't resist an itch. This will help prevent bacterial conjunctivitis (which requires innoculation of the eye directly) and viral conjunctivitis (which usually spreads from the nasal cavities). Talk to your physician about medications that reduce the symptoms of seasonal allergies if your conjunctivitis is allergenic, or find some way to avoid whatever allergens you can't deal with.Tuckerekcut 22:46, 15 December 2006 (UTC)

Categories: Reference Desk Archives