Wikipedia:Reference desk/Archives/Science/2009 September 9

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September 9

Energy content

Which has the most energy if were to be released in the most efficient manner: 1kg of gasoline or 1kg of hydrogen? —Preceding unsigned comment added by 79.75.14.110 (talk) 00:41, 9 September 2009 (UTC)

Per the lead paragraph of our article on energy density, "hydrogen has a higher energy density per unit mass than does gasoline, but a much lower energy density per unit volume." However, for the strictest possible interpretation of "most efficient manner" (that is, matter-antimatter annihilation), they'd be identical, as mass is the only consideration in such a case. — Lomn 00:43, 9 September 2009 (UTC)

I think the OP meant the most amount of work you can extract in the most efficient manner from those 2 - otherwise efficiency doesn't mean much (as Lomn pointed out). --antilived^{T | C | G} 01:14, 9 September 2009 (UTC)

The work done by an engine typically comes from heat energy produced in some exothermic reaction, so you could do work by annihilating hydrogen or gasoline just as you could by burning them (and a lot more of it). Rckrone (talk) 03:11, 9 September 2009 (UTC)

I think you might have some trouble finding anti-gasoline... --antilived^{T | C | G} 05:09, 9 September 2009 (UTC)

I leave details like that up to the engineers. :) Rckrone (talk) 05:35, 9 September 2009 (UTC)

Which is why we engineers say: "What a bloody stupid answer, the OP is CLEARLY not talking about matter/antimatter or direct matter-to-energy conversion."...this is merely confusing an otherwise clear answer - which is "Hydrogen, by mass. Gasoline, by volume." SteveBaker (talk) 13:34, 9 September 2009 (UTC)

Steve, I'm not sure if I should take offense at this or not (particularly as an engineer). I led the original answer with precisely "hydrogen by mass, gasoline by volume", and then added antimatter as the addendum. — Lomn 16:27, 9 September 2009 (UTC)

Then the question devolves into a request for clarification about the intended meaning of "efficiency" - if the OP meant thermodynamic efficiency, then Lomn's theoretical answer is valid. If the OP meant "practical, realizable, efficient combustion in an engine, in 2009", then clearly an analysis of matter-antimatter reactions is irrelevant. Again, the practical considerations start to become convoluted by details other than the raw thermal energy released from oxygen-fuel combustion: does manufacturing and carrying around the necessary, custom equipment to perform hydrogen combustion count against the overall "efficiency" score, or are we again only talking about the net energy released? Fuel efficiency will suffer, because 1 kg of hydrogen can not be stored as easily (ergo, as "efficiently") as 1 kg of gasoline. The OP did not state explicitly, but I think their question was implicitly asking for the molar heat of combustion, normalized by the mass-per-mole, for oxygen-fuel combustion of 1 kg each. The answer to this question was helpfully provided and referenced below, by 83.100.250.79. Nimur (talk) 17:50, 9 September 2009 (UTC)

You don't need "anti-gasoline"; any antimatter will do. — Lomn 12:58, 9 September 2009 (UTC)

I would combine a unit mass of hydrogen plus unlimited oxygen for the one case, and the same unit mass of gasoline plus oxygen for the other case. Chemists are welcome to chime in with respect to the energy liberated in each case. Naively, I would bet on hydrogen. Edison (talk) 02:40, 9 September 2009 (UTC)

Enthalpy of combustion:

Gasoline ~45MJ/kg [1]

Hydrogen 143MJ/kg (@286kJ/mol , 2g/mol , 1000g/kg Hydrogen) —Preceding unsigned comment added by 83.100.250.79 (talk) 05:36, 9 September 2009 (UTC)

And just for fun semtex exploding gives about 4 MJ/kg. But of course the clever thing about semtex was not the energy yield but the fact is couldn't be detected by a sniffer dog... --BozMo talk 13:20, 9 September 2009 (UTC)

Nerves and eyes

Pathways from eye to brain, with midline-crossing pathways in blue, and ipsilaterally projecting pathways in red.

Most parts of the body are connected to the "other" side of the brain, so the right leg is handled by the left brain, et cetera... I know this is different for the eyes, but are they entirely the same side, do the muscles go with one and the optic nerve with the other, or some combination? SDY (talk) 02:17, 9 September 2009 (UTC)

Through the marvel of hemidecussation, the left half of each retina goes to the left hemisphere and contrariwise. It is said to be a sharp split at the center of each retina. Not sure how the fovea centralis splits, but presumably the same. This shows up in the Michael Gazzaniga experiments with split brain patients. If an object is to your left, it is processed by the right hemisphere, and the left hemisphere knows of it only if the corpus callosum has not been severed. Optic fibers cross over at the optic chiasma. In movies of split-brain patients, the hemisphere controlling speech would produce verbalizations which were mere guesses regarding visual stimuli presented to the other hemisphere, but the non-speaking hemisphere would cross-cue by shaking the head, whereupon the speaking hemisphere would change to the answer the nonspeaking hemisphere had seen. We seem to have two brains, each quite capable on its own. Edison (talk) 02:33, 9 September 2009 (UTC)

(ec) Our article on the optic chiasm explains this, although not very well. Basically, both eyes send some input to both sides of the brain. The way I always remember it is each side of the brain gets input from the opposite side of the world. The right side of the brain gets input from the left side of the world; the left side of the brain gets input from the right side of the world. If you work it out, the consequence is that the left side of the retina in both eyes projects to the left side of the brain, and the right side of the retina in both eyes projects to the right side of the brain. This arrangement may seem bizarre at first, but it has the very useful property of causing the visual input to each side of the brain to come from the same place where tactile input to that side usually comes from, and where motor output from that side goes. Looie496 (talk) 02:41, 9 September 2009 (UTC)

And where is the actuation of eye muscles centred? --Tagishsimon (talk) 02:43, 9 September 2009 (UTC)

In many different nucleii, which is why a neurologist can tell so much about the state of your brainstem by evaluating the status of your extra-ocular muscles. - Nunh-huh 02:50, 9 September 2009 (UTC)

(ec again, yikes) The "final common pathway" for eye movement is a set of small brainstem nuclei, but huge areas of the brain are involved in eye movement control. By the way this picture is a beautiful illustration of the left-right pathways, too bad we don't have one as nice. Looie496 (talk) 02:53, 9 September 2009 (UTC)

It might be useful to note here that while one-sided numbness and paralysis caused by stroke is evidence of a defect in the opposite side of the brain, blindness in either eye caused by stroke is associated with a defect in the same side of the body as the eye.Mrdeath5493 (talk) 07:12, 9 September 2009 (UTC)

Higgs boson

Why does interaction with the Higgs field create inertia, but interactions with vector bosons, such as the photon, gluon, and W and Z bosons do not have this effect? 70.24.36.158 (talk) 03:06, 9 September 2009 (UTC)

Because different fields and particles interact in different ways, according to the Standard Model, to give a glib non-answer. It's just how the maths of the theory works. See Spontaneous symmetry breaking and Yukawa interaction for more details. Fences&Windows 04:33, 9 September 2009 (UTC)

Can you give a semi-technical overview of the math involved, or is it too complex? 70.26.154.210 (talk) 01:20, 10 September 2009 (UTC)

They do have that effect. Most of the mass of ordinary matter (~90%?) comes from the strong force, and most of the rest from kinetic energy of the quarks. All other contributions including the Higgs interaction are a small (~1%?) correction on top of that. I think the W and Z bosons also get small masses from QCD (the Higgs mechanism article says they do). However the masses you get this way don't match what is observed, and the Higgs field was introduced to make up for that difference. The Standard Model attributes all mass discrepancies to the same Higgs field, though you could explain them in other ways (like additional Higgs fields or, in most cases, explicit mass terms). I'm not sure where the idea came from that the Higgs field is the source of all mass. It would be better to say that the Higgs field is the source of all the mass that we don't understand. John Baez points out that of ~25 adjustable parameters in the Standard Model, 22 describe the Higgs or its interactions with other fields, so it's probably hiding a lot of beyond-Standard-Model physics. -- BenRG (talk) 17:53, 9 September 2009 (UTC)

The answer to that question really depends on whose mass you are talking about. As BenRG pointed out above, if you are talking about the mass of a bound state (not a fundamental particle), like a proton or an atom, the energy of the vector bosons responsible for the bonding does indeed contribute to the mass of the bound state. On the other hand, if you are talking about the mass of the fundamental particles (quarks, leptons, W, Z, and the higgs itself), the vector bosons do not contribute. The reason for that is the fact that the ground state (state of minimal energy) of the vacuum of the theory correspond to a non-vanishing higgs field. It is said that the higgs has a non-vanishing vacuum spectation value (VEV). The vector fields MUST have vanishing VEVs (otherwise Lorentz invariance would be spontaneously broken) and therefore they do not contribute to these masses. Dauto (talk) 15:50, 11 September 2009 (UTC)

Pass the veggie dogs please!

I've been a vegetarian for 14 years, for ethical reasons. My family had dogs when I was growing up, but I never had my own dog as an adult until now. (The arrangements have been made; she'll be coming to live with me in a few weeks.) I would like her to live on a vegetarian diet as well. What I'm wondering is this: Can a dog truly be as healthy on vegetarian dog food as on regular dog food, or is there still some legitimate controversy about that? How much more expensive is it to keep a dog on a vegetarian diet? The dog is about three years old and has been eating a non-vegetarian diet up to this point; would that present any particular problems or challenges? - Lydia's Alpha-to-Be —Preceding unsigned comment added by 71.104.238.248 (talk) 03:37, 9 September 2009 (UTC)

Well, some people at least maintain that some dogs can thrive on vegetarian or vegan diets. Watch out for dilated cardiomyopathy due to L-carnitine or taurine deficiency. Never own a cat. - Nunh-huh 04:04, 9 September 2009 (UTC)

Do vegan dogs have an increased tendency to eat cats? 124.154.253.31 (talk) 04:17, 9 September 2009 (UTC)

I wouldn't be in the least bit surprised, but what I meant was that feeding a cat a vegan diet would be abusive. - Nunh-huh 05:39, 9 September 2009 (UTC)

Dog#Diet says they are at least capable of doing so, but you should contact a vet for his/her advice. --antilived^{T | C | G} 05:07, 9 September 2009 (UTC)

Yes, I'm well aware that cats are carnivores and aren't biologically equipped to eat a plant-based diet, and if I ever did happen to have a cat in my life, I would respect that and buy something meat-based. However, since dogs are omnivores (like humans) I've heard that they can thrive on a vegetarian diet. Of course, the typical diet of canines in the wild has more animal protein than that of primates in the wild, so I don't imagine it would be a strict equivalence. Of course I would talk to the vet before making the final decision on Lydia's diet (and I could always make a change one way or the other based on her health, our finances, new advances in dog food, etc.), but I just wanted to get an idea early on, while we still have a couple months to figure out exactly how she's going to fit into our lives. Thanks for your answers! - Lydia's Alpha-to-Be —Preceding unsigned comment added by 71.104.238.248 (talk) 06:47, 9 September 2009 (UTC)

Dogs are indeed omnivores - not herbivores - their primary diet is meat - although they'll eat vegetable matter if they are hungry enough and there is nothing else available. Humans are also omnivores - but our primary diet isn't (or at least, shouldn't) be meat. So we do much better on an artificially herbivorous diet than dogs do. I don't think it's fair on the dog to try to make it be what it isn't. Trust me - dogs have no ethical desire to avoid eating meat. Even our 10 year old labrador - who is the gentlest, most mild-mannered dog you'll ever meet - has absolutely no compunction in chasing down a squirrel, ripping its head off and feasting on it's still warm-and-twitching body. If you don't like that dogs behave like this - then the remedy is for you to avoid owning one - rather than trying to change it's ethics to match yours. Dogs eat meat and chew bones...it's what they do...it's by FAR their greatest joy in life...it's what they live for. SteveBaker (talk) 12:58, 9 September 2009 (UTC)

I agree with SteveBaker. While an ovo-lacto-vegetarian diet won't kill a dog (the way it will a cat), it's really unfair, maybe even cruel, to the dog to force it into a dietary lifestyle it's incapable of understanding or appreciating. If you were still at the point of merely considering getting a dog, I'd advise you to get a rabbit or guinea pig or some other thoroughly vegan pet instead. As it is (your getting a dog is now irreversible), please allow your dog to eat what makes her happy, the same way you eat what makes you happy. +Angr 14:03, 9 September 2009 (UTC)

Agreed. I very much doubt that domestic dogs, cats and whatever else really care enough about their owners' moral, ethical, religious or socio-political views to make personal sacrifices. --Kurt Shaped Box (talk) 14:40, 9 September 2009 (UTC)

On the other hand, How much meat do pet dogs usually get anyway? Aren't most cheap dog foods little more than vitamin enriched, meat flavored, corn meal? A quick look at some ingredients lists leads me to believe that some of the popular brands are mostly grains with some lard mixed in for flavor. If the brands of vegan dog food on the market have found some good replacement for the lard flavor (have they?), then how's the dog even going to know?

(Personally, I still wouldn't try it with a cat. The risks are a lot higher, and I frankly don't trust quality-control on pet foods at all. But what do I know? I've never had any particular inclination to make myself a vegetarian, let alone a pet.)APL (talk) 14:51, 9 September 2009 (UTC)

I'm no vet, so this advice is worth as much as you have paid... This site seems to give some decent advice: "Dogs love meat and they need protein". -- Александр Дмитрий (Alexandr Dmitri) (talk) 15:40, 9 September 2009 (UTC)

As pack animals, dogs will be loyal to you no matter what you put them through - but you have a responsibility to return the favor by keeping them happy. Dogs are the least vegetarian animals I can think of! The evidence of their carnivorous tendencies is everywhere. It's not about dog food...most of the dry food doesn't look like it's ever been need an actual animal. That's not the point. Dogs need to chew to keep their teeth in good shape - the various plastic toys and fake bone-like products don't seem to interest them much. That means that they need real bones and chewable rawhide toys and things like (my dog's favorites) pig ears just to keep their teeth healthy. Our dogs occasionally get those two foot long cow bones - which they'll (hilariously) laboriously haul around the house and try to hide from each other as they gradually gnaw this 10lb bone down to nothing over a period of weeks. One of those will entirely consume their waking hours for almost that entire time - it's hard to imagine how they are not utterly passionate about that behavior. When dogs sleep - you can see their feet twitching and they make tiny dream-barking noises as their jaws move and their cheeks puff out...then you see their jaws moving with little dream biting and chewing motions. There can be little doubt that they even DREAM of hunting small furry animals. Truly - find a good home for your dog and get a rabbit (I recommend an English rabbit) - they are very cool: you can train them - treat them like a cat or small dog - and feed them vegan stuff and they'll be very happy and healthy.) SteveBaker (talk) 15:55, 9 September 2009 (UTC)

Anecdotally, a friend of mine in Scotland, who had grown up on a working farm with dogs and was in addition a bright and unsentimental woman, fed her Alsatian and Golden Retriever on a vegetarian diet, carefully balanced, with appropriate added supplements, and bones to gnaw. My friend was not herself a vegetarian, and I can't remember her specific motivations, but the two dogs (whom I often looked after) thrived physically and mentally, and their faeces were markedly less smelly than is generally the case with meat-fed dogs. I agree that one should not do this without specialised knowledge and/or vetinarian advice. As it happens, another Scottish friend, my landlady for a time, kept a wild rabbit (rescued as a kit) as a perfectly contented and agreeable house-pet in her upstairs flat, though I agree an outside hutch might be considered more usual. 87.81.230.195 (talk) 19:00, 9 September 2009 (UTC)

The key there is probably the "and bones to gnaw" part. If bones are large, fresh and uncooked (required to avoid choking risks) - the dogs get a good deal of nutrition and 'meaty stuff' from the marrow inside the bones. If she had cut off the bone supply - I'd imagine the problems would begin right there. On a farm, the dogs may well have been 'self feeding' too - catching rabbits and squirrels, rats & mice - that kind of thing. SteveBaker (talk) 20:15, 9 September 2009 (UTC)

On the subject of dogs and bones, do you remember a time a few years back when 'they' were saying that dogs should never be allowed to gnaw on bones - due to the risk of sharp bone splinters being swallowed and causing internal injuries? I don't know if that was just one particular school of thought on the matter (I've never owned a dog, so I wasn't really paying it a huge amount of attention) but I definitely remember 'dog experts' on TV saying it several times. --Kurt Shaped Box (talk) 20:37, 9 September 2009 (UTC)

Wasn't that strictly for poultry bones? And seriously, if bones were regularly killing dogs, wouldn't we have ended up evolving dogs that did not engage in such dangerous behavior? 65.121.141.34 (talk) 21:16, 9 September 2009 (UTC)

The issue is with thin cooked bones. Cooked chicken bones are certainly not good - raw is fine though. Large bones are OK cooked. Dogs have evolved to gnaw bones - that's why they have not evolved toothpaste. SteveBaker (talk) 02:38, 10 September 2009 (UTC)

I would say that your primary ethical consideration here is to that one living creature you are bringing into your life, not to every other living thing on Earth whose life you wish to spare also. This is especially so since a dog will give you unconditional love and devotion and do anything to be part of your "pack". Dogs will eat pretty much anything, and most are also incredibly stoic, so they won't show signs of dicomfort until they have gotten pretty sick. While it certainly may be possible to create a perfect vegan dog food, the danger I see is in subtle deficiencies building up over time, such as the cardiomyopathy mentioned above. She won't tell you about her discomfort until it's too late. The safest way to go IMO is to use the highest quality of food you can afford, and don't worry about the meat components too much. Meat should always provide the best balance of nutrients for a dog, it's what they've been eating for thousands of years. It's true that they'll find certain types of grass and spend 20 minutes eating them (fibre? micronutrients?), and it's true that they'll eat any kitchen scrap you give them (mostly because they've been staring at you while you cook, trying to figure out how to get up on the counter where the human food is) - but if they can catch a squirrel, they'll ignore the corn cobs.

And if your dog is used to one type of food, you should be very careful if you're changing over to another, their guts will be set up to process the food they're used to. Franamax (talk) 20:17, 9 September 2009 (UTC)

Start by giving the dog the same diet as it has been used to - enough trauma with the move itself. Then using the many thoughtful suggestions above, gradually alter the dog's diet to one that is more in keeping with your beliefs. Abrupt diet changes can cause intestinal distress resulting in diarrhea and you wouldn't want that along with all of the other distress of a having a new household member. hydnjo (talk) 21:18, 9 September 2009 (UTC)

Making the dog of a vegan eat only a vegan diet, which it would not choose if given a choice, is a bit like baptising the dog and feeding it the eucharist. Or declaring the dog is an athiest, or a Tory. The moral choice of avoiding meat and animal products just will not give the dog the moral glow it gives the human. My father would feed his hunting dogs steak which had gone out of date in the freezer of a restaurant, but they also ate cornbread he baked for them. They would also eat green plants they found in their prowls. The vet's advice is the thing to give heed to. Edison (talk) 22:50, 9 September 2009 (UTC)

I think this, and all similar sentiments above, is missing the point. Sure, the dog won't have the same moral objection toward eating meat that a vegetarian or vegan might have. But this is irrelevent. Some dogs don't apparently have moral objections to mauling children, but we don't let them get away with that while saying things like "well we might feel morally happy about not mauling children but the dogs don't share our viewpoints". Very few, if any, ethical vegans or vegetarians are going to hold the belief "it is wrong for me to cause the suffering and death of animals but it is fine for everyone else". Most ethical vegans or vegetarians will think "it is wrong for anybody to cause the suffering and death of animals" and they will acknowledge that it happens "in the wild" but view this as an unfortunate result of evolution. Someone who owns a dog has every right and is, indeed, behaving quite admirably, to want to give their own dog a healthy lifestyle with minimal impact on the lifestyles of other creatures. Maelin (Talk | Contribs) 06:40, 10 September 2009 (UTC)

When a dog urinates on a fire hydrant, he is not committing vandalism, he is just being a dog. Don't force your moral beliefs on your pet. It will not understand. Googlemeister (talk) 13:17, 10 September 2009 (UTC)

Seems to me that any moral or ethical vegan wouldn't even consider the concept of "owning" a dog. Is it OK to own a slave, so long as you feed it only carrots? "Someone who owns a dog has every right and is, indeed, behaving quite admirably..." - that's quite a statement of beliefs right there. Maybe this would be better addressed at the Humanities desk? As far as SciRef goes, the general advice here seems to be that meat is the better way to go. Taking ownership of an animal and then forcing that animal not to ever eat another animal as an expression of your love for animals? Ackk - something missing in that equation. Franamax (talk) 11:18, 11 September 2009 (UTC)

How to charge the batteries and measure current?

Hello friends!, I know a lot of methods still available to measure the current stored in a Battery. But i need a simple method or atleast understandable. I have 4 AA size 1.2V, 850mAh NiCd batteries. I designed a charger circuit with charging voltage of 5V and charging current of 240mA for 4 batteries in series. So that each battery gets 240/4 = 60mA. Since my battery has 850mAh rating, now I don't know how long do I have to charge or how much charging current is actually needed?. I need atleast 4.8V,250mA for my main project ciruit to work.And my batteries with the above rating doesn't even supply power for more than 10 minutes even when it's been charged for more than 8 to 10hrs. So with my current battery rating,the backup should atlaeast last for 3 hours?What could be the problem?. In charger circuit, I use a 22 (1 watt)Ohm current limiting resistance in series with the input 5V source to get a current of 240mA. All 4 batteries are connected in series while charging.when I read the voltage of the battery, it shows 1.26V(1 battery) when charged fully and 1.1V when everything was drained!. For my main project, it consumes 250mA current with 4.8V requirement. ...In my case, is the battery actually charging or do I need more current rating for my design.? Please help me —Preceding unsigned comment added by Balan rajan (talk • contribs) 05:29, 9 September 2009 (UTC)

Current is not stored in a battery, charge is. The rating is for milliampere-hours, which (someone check my math) 1 milliampere-hour = 3.6 coulombs. A battery with a rating of 850 mAh will supply a current of 1 milliampere for 850 hours, or 850 milliamperes for 1 hour, or some combination thereof, such that milliamperes X hours = 850. The time to charge the battery will depend a lot upon how much current the charger itself operates on. Assuming a perfect system, if your charging current is 60mA (240 mA divided by 4 in series, if I am reading that right), then the battery should be fully charged in 850/60 = 14 hours, ten minutes, give or take. It will probably take somewhat longer than that given inherent losses in the system, so lets say 16-17 hours for a full charge. 8-10 hours would not nearly be long enough. Also, you do not indicate what your discharging circuit current is. If I draw 8.5 amps out of a fully charged, 850mAh rated battery, it'll be fully drained in 6 minutes... SO it looks like a combination of a) not enough charging time and b) too high a load on the battery when being discharged. --Jayron32 05:47, 9 September 2009 (UTC)

Although not as explosive it actually takes more a complex design to charge NiCd/NiMH batteries than Li-ion ones. Seeing that you probably aren't too advanced in electronics (all components get the total current if they're series, see Kirchoff's circuit laws), you should probably use an off-the-shelf charger for now. Also, batteries don't have perfect reciprocity, they tend to drain a lot faster under high current (ie. 1mA load might last 850 hours, but 850mA load probably won't last an hour), so you should take that into account too. --antilived^{T | C | G} 11:28, 9 September 2009 (UTC)

Well, you're probably not charging the batteries at all - that's the problem. The best way to charge NiCads is to use a constant current source, not a constant voltage source, as you're trying. Commercial chargers provide this, which is why they're better. As you describe your set up, you have 4 ~1.2V batteries in series, a total of ~4.8V. That voltage is dropped by a 22 ohm resistor, meaning that the current flowing is I=V/R=0.2/22=9mA. With this current, they'll take about 100 hours or so to charge. As the batteries charge, their voltage will increase slightly and so the current will drop further and the charging will take longer. So we see this circuit just won't work. With a constant current charger this problem does not occur. It's then easiest to work out when they're fully charged by feeling them - they will get slightly warm when they have charged up. --Phil Holmes (talk) 14:38, 9 September 2009 (UTC)

There is a limit to how fast a battery should be charged or discharged to avoid damage, explosion, or shortened service life. Isn't there some rule of thumb of using the ampere hour rating divided by 10 to get a charge rate for Nicads? That would imply 85 ma for 10 hours to charge the 850 mah cells. The charge should taper off so that the current drops to a mere trickle when the battery is are charged, rather than continuing to raise to voltage to force the same current through a fully charged battery. That would eventually cause loss of moisture in the electrolyte, outgassing, overheating, and explosion unless the venting system was adequately vented. Edison (talk) 22:41, 9 September 2009 (UTC)

C/10 makes a good charging rate. The problem with trying to reduce the current when the batteries are nearly charged is that it's hard to tell when NiCads are nearly charged. The normal way is genuinely to check whether they're warm. This can be done with a thermistor to automatically cut the charge, or by hand when you expect they will be charged (after about 14-16 hours, if fully discharged). Providing they are checked frequently they will not suffer significant damage. --Phil Holmes (talk) 08:54, 11 September 2009 (UTC)

I couldn't understand his calculation..."you have 1.2V 4AA batteries in series, a total of ~4.8V. That voltage is dropped by a 22 ohm resistor, meaning that the current flowing is I=V/R=0.2/22=9mA. With this current, they'll take about 100 hours or so to charge. As the batteries charge, their voltage will increase slightly and so the current will drop further and the charging will take longerWhy does he substitue v=0.2v in this calculation?. Applying 4.8V as the charging voltage across 4 AA batteries with a current limiting resistance of 22Ohms in series will charge a battery with V = 1.2V and I = 1.2/22 = 54mA. But he says the battery will be charged at 9mA. Could you explain (Phil Holmes) what it means please?. —Preceding unsigned comment added by Balan rajan (talk • contribs) 09:21, 12 September 2009 (UTC)

In your original post, you say you have the batteries in series. That means that the negative electrode of one is attached to the positive electrode of the next, so they are effectively stacked on top of each other. Their voltages therefore add up, so the total voltage across 4 cells in series is 4.8V. The full current flows through each battery, in effect one after the other.

You may have meant that they are in parallel - i.e. with all the negative terminals connected and all the positive ones. In this case, the voltage across them would be 1.2V, and any charging current would be shared. However, charging them in this way would also mean that it's unlikely that each will be properly charged. The current will not flow equally through all 4 and you will end up with one getting over-chrged and another not being properly charged. I would re-iterate a previous comment - if you do not understand the concept of series and parallel properly, you probably should not be trying to make a battery charger which could potentially cause the batteries to explode. Buying a commercial one is likely to be cheaper in the long run. --Phil Holmes (talk) 10:01, 12 September 2009 (UTC)

Glucose oxidation

I'm rephrasing the question because it seems that it wasn't completely clear the last time around.

The oxidation of glucose to CO2 and water has a very large accumulative G0' value and yet glucose is quite stable in the presence of oxygen, why is this so?

I'd appreciate it if a scheme of the glucose oxidation reaction could be added with a full description of what happenes energy-wise and so on. —Preceding unsigned comment added by 93.183.239.108 (talk) 13:49, 9 September 2009 (UTC)

Activation energy - most things are unstable with respect to something else, but the activation energy prevents the reaction happening without extra heat, a catalyst, etc..83.100.250.79 (talk) 14:00, 9 September 2009 (UTC)

Another way of looking at it; while the thermodynamics favor the formation of product, the chemical kinetics is not favorable to spontanaity due to the large energy barrier (Activation energy) towards forming the oxygen-glucose activated complex necessary for the reaction to proceed. --Jayron32 18:07, 9 September 2009 (UTC)

(ec)The editor above is absolutely correct. The stability is because at room (or body for that matter) temperature, there is insufficient energy to overcome the activation energy. Gasoline, or even hydrogen mixed with oxygen has incredible potential energy, but the activation energy is such that the mixture can exist for an indefinite period of time. Something either needs to bring the energy above the activation energy, such as a spark provided to the fuel-oxygen mixture, or the activation energy needs to be decreased, such as with the presence of an enzyme. Glucose is oxidized through a series of reactions, using a large number of highly specialized enzymes, each of which not only lowers the activation energy so the reaction can proceed, but also ensures only the desired product results from the reaction. Enzymes not only allow the reaction to proceed at the temperatures present in a biological system, but also prevent the ligands from reacting with or into any undesired chemicals. The Seeker 4 Talk 18:14, 9 September 2009 (UTC)

How can matter exist?

From my understanding of chemistry (mostly learned a few years ago in high school), I do not understand how matter can exist if the protons and electrons are so small in the atoms that make up matter. I skimmed the atom page, but didn't see any real answer, although there probably isn't one yet. How can matter exist if there's basically nothing in the atoms (correct me if I don't know what I'm talking about = ])? EVAUNIT-666 18:24, 9 September 2009 (UTC)

Next to nothing is not the same as nothing. And if you cluster a sufficiently large quantity of next-to-nothings together, you get something substantial. Baseball Bugs ^{What's up, Doc?} carrots 18:30, 9 September 2009 (UTC)

(EC with bugs)Fundemental particles (the quarks that make up protons and neutrons, and leptons of which the electron is one example) are essentially point-particles(dimensionless). However, the interactions between these particles occurs at measurable distances, and the distances of those interactions defines the size of things like atoms and molecules. So, even though the parts that fundementally make up an atom have no size at all, because these particles exist at a definable distance, THAT distance defines the size of the atom, which in turn gives volume to matter. For example, though an individual electron is essentially volumeless, the electrons orbit an atom in the electron cloud, the interactions between electrons and protons, and between electrons and each other define the size and shape of this cloud, and THIS is what gives an individual atom a real volume (see atomic radius. Put a group of atoms together, and they way that they interact with each other defines the bulk volume of matter, and thus you have the world you see around you.

See standard model and Fundamental interaction for more on these sorts of interactions between fundemental particles. --Jayron32 18:36, 9 September 2009 (UTC)

Does the solar system exist? Most of the solar system is not occupied by planets, moons, or other heavenly bodies. Does a galaxy exist? Even though stars can be thought of as large, most of the galaxy (I think) is composed of fairly empty space.

Furthermore, the speed of electrons, combined with their very small orbits, places them almost "everywhere at once." I think this gives the substantiality to matter.

One finds it difficult to walk through walls not because the wall or the person is terribly dense, although the person could be dense in a different sense, but rather because of the likelihood that the fast moving electrons comprising the atoms of the of the human will "just happen" to be in a position in their orbit to encounter the fast moving electrons in the atoms comprising the wall. Bus stop (talk) 18:56, 9 September 2009 (UTC)

So, when Superman walked through a wall in one of the 1950s TV episodes, he was probably defying the laws of physics? Baseball Bugs ^{What's up, Doc?} carrots 19:06, 9 September 2009 (UTC)

Nonsense! Superman was always perfectly law-abiding. They probably just hadn't passed that law yet, I imagine it was still stuck in committee. (Superman really wasn't that good at politics). Franamax (talk) 19:42, 9 September 2009 (UTC)

Forgetting the ongoing absurdity of a man flying, "The Mysterious Cube" has to be in the top echelon of the most preposterous episodes in the series. A scientist friend of Superman's convinces him that he could pass through solid objects, through the power of super-concentration. Now, maybe that could be theoretically possible, given that Superman can fly faster than light and see through anything (except Lois' dress). All well and good. Except that when he passes into the ultra-dense material comprising the cube, his suit comes with him. Apparently his super-suit had a mind of its own. Baseball Bugs ^{What's up, Doc?} carrots 03:41, 10 September 2009 (UTC)

It's best not to worry about such things. --Tardis (talk) 14:35, 10 September 2009 (UTC)

Thinks look solid - because even though they are mostly vacuum - they still block and reflect light perfectly well. They feel solid because the electrons in orbit around the atoms of that chair you're sitting on are negatively charged and they repel the negatively charged electrons of your rear-end. Hence things feel solid. The mass of the atom is almost entirely centered in the middle...but they weigh what they should - so they are heavy enough to seem solid. Between those things - matter does indeed behave like it was solid. However, truly "solid" materials - something like a neutron star - which have all of the atoms squished together without all of those gaps - seems like really bizarre 'stuff'. As our article points out - the entire mass of all of humanity - crushed to the density of a neutron star would be smaller than a sugar cube. Neutron stars have so much gravity that they bend light by enough that you can stand 'in front' of one and see all the way around the back of it! SteveBaker (talk) 20:10, 9 September 2009 (UTC)

The basic reason that matter occupies space is the Pauli exclusion principle. There's a short discussion at Pauli exclusion principle#Stability of matter. Electromagnetism is involved, since it's the electromagnetic force that determines the available orbitals, but it's not an electromagnetic contact force that prevents you falling through the floor—I'm pretty sure of that. Electrons aren't pointlike in any sense that matters here. They effectively fill the available space as far as the Pauli exclusion principle is concerned. The nuclei are relatively well localized with large gaps between them and they contain most of the mass, so in that sense you can say that ordinary matter is mostly almost-empty space, but not in any other sense. -- BenRG (talk) 13:45, 10 September 2009 (UTC)

Helen Keller got it right. She was talking about humans, but she may as well have been talking about atoms: Alone we can do so little. Together we can do so much. -- JackofOz (talk) 21:15, 10 September 2009 (UTC)

How fast do interstellar dust clouds move?

More dust

NASA just released a whole bunch of new space images, like the butterfly here: http://www.wired.com/wiredscience/2009/09/hubble_gallery/.

If we take another picture of this 100 years from now, will it look any different than it does now? How long would it take to be noticeably different?

Thanks! — Sam 63.138.152.155 (talk) 18:50, 9 September 2009 (UTC)

That "butterfly" is a planetary nebula. Planetary nebula#Lifetime has some relevant information - they are very short lived by astronomical standards. --Tango (talk) 18:58, 9 September 2009 (UTC)

Well, indeed, but the article you cite says "They are a relatively short-lived phenomenon, lasting a few tens of thousands of years." A few tens of thousands of years is actually a very long time by our standards. So I'm guessing that in a hundred years another picture of the formation might look almost identical? — Sam 63.138.152.155 (talk) 19:03, 9 September 2009 (UTC)

For the linked picture of the butterfly (often called by its less romantic name, the Bug Nebula), the explosion which created the nebula occurred roughly two thousand years ago. The expanding cloud is now (mostly) a very, very long way from its parent star, so it feels very little gravitational attraction and will be moving outwards at a (nearly) constant rate. So, figure in another hundred years the nebula will be about five percent broader, and a little bit dimmer. The difference will be perceptible (if you have two photographs, side by side) but not particularly dramatic. TenOfAllTrades(talk) 19:36, 9 September 2009 (UTC)

The pillars in that photo at right are about 100 Trillion kilometers tall. The dust would have to be moving at an impressive speed for the picture to change very much in 100 years! SteveBaker (talk) 02:35, 10 September 2009 (UTC)

Oxymuriate of mercury

This substance is frequently mentioned in nineteenth-century medical texts - what's it's modern name? Mercury (II) chloride is one obvious suggestion, but that's "corrosive sublimate", and the "oxy" might suggest it contains oxygen. Thanks in advance. Tevildo (talk) 21:57, 9 September 2009 (UTC)

An oxymuriate is a salt of hydrochloric acid - the term comes from times when all acids where though to contain oxygen, unfortunately I can't find a wikipedia page on the history of the understanding of acids. Wait see Acid-base_reaction_theories#Lavoisier_definition 83.100.250.79 (talk) 22:20, 9 September 2009 (UTC)

See http://dictionary.reference.com/browse/oxymuriatic ,

To confuse things oxymuriatic acid is actually (probably) chlorine gas. see [2] this is Humphrey Davies discovery that chlorine gas (oxymuriatic acid) is not what it was thought it was.. 83.100.250.79 (talk) 22:27, 9 September 2009 (UTC)

They are the same thing [3].83.100.250.79 (talk) 22:31, 9 September 2009 (UTC)

how trained are drug dealers/makers in organic chemistry, usually?

Just curious. (Not being a gangster myself of course.) I suppose there are the drug dealer versions of script kiddies who just follow recipes, and actual gangstas who know what's going on? John Riemann Soong (talk) 22:07, 9 September 2009 (UTC)

Drug dealers are usually members of a union or professional organisation, such as the Royal Society of Skag Peddlers. Their websites will probably have statistics on the qualifications of their members.

As far as I know, cocaine isn't worth synthesising from scratch, so the chemistry is pretty basic acid-base reactions and purification. LSD requires a bit of tinkering, and MDMA is a proper synthesis job.

Apparently, most LSD produced in America is made by a handful of experienced chemists in northern California, many of whom have been at it since the sixties. They can get away with it because there are so few of them, they all know each other, and they only make small quantities (because that's all you need, it seems). I once read that federal agents uncovered a drug production lab housed in a grain silo buried underground.

I reckon the overall answer is this: most drug producers don't know loads, just what they need to. But certain drugs need skill to make, and are made by a few specialists.

Ben (talk) 22:34, 9 September 2009 (UTC)

I would guess, not very. You don't need much formal training is chemistry to just follow a recipe and make the drugs. The training is required to do research and come up with new knowledge (about new chemicals, new ways to make old chemicals, explanations of why certain things are the way they are, etc.). Drug manufacturers don't generally do that kind of stuff. It is similar to how you don't need to be an automotive engineer to work in a car factory. --Tango (talk) 22:42, 9 September 2009 (UTC)

I'm curious whether the field would weed out those who didn't have some sort of (non-monetary) interest in science (albeit black market science)? Actually my main reason of wondering this was just as Malcolm X thought his bookie would've been a NASA scientist if he had been born white, whether many of the "top" drug makers would've been found in top schools had they been born into more privilege. Presumably, the less skilled you are (or the less you know what's going on), the less your purity and the less your yield. (higher grade => higher prices?) John Riemann Soong (talk) 22:49, 9 September 2009 (UTC)

A chapter of Freakonomics discusses the retail (not manufacture) of illegal drugs in a Chicago housing project. JT (the area manager for the Black Disciples gang) is a college graduate who could evidently, in other circumstances, have done well for himself in the licit business world, and who runs the gang like a Harvard Business School grad. -- Finlay McWalter • Talk 23:01, 9 September 2009 (UTC)

Relevant articles are clandestine chemistry and Uncle Fester (author) (and for the more experimental, PiHKAL). Meth labs are particularly prone to explosion (video), which I think is evidence that production is mostly done by people who're mostly following an underground folk-recipe (rather than being skilled lab chemists). They may also be breaking Lopez' law: "don't get high on your own supply". -- Finlay McWalter • Talk 22:53, 9 September 2009 (UTC)

The lack of safety is probably due to lack of skill, but it could also be because of poor equipment. (Given the amount of money you can make out of producing meth you would think they could get good equipment, but not doing that would be poor business skill rather than poor chemistry skill.) --Tango (talk) 13:28, 10 September 2009 (UTC)

I just want to note that it REALLY depends on the drugs in question and the type of manufacture. As far as I can tell there are entirely different methods of production and people involved in the production of cocaine, LSD, ecstasy, and methamphetamine, and the skill required is likely quite different as well. My suspicion is that in terms of theoretical knowledge, meth makers are probably pretty low on the list—any old hillbilly seems able to set up a meth lab (albeit not the most safe one). --98.217.14.211 (talk) 23:55, 9 September 2009 (UTC)

The meth synthesis is easy if you start with pseudoephedrine, which comes from decongestant pills. People who do that generally just follow recipes. I don't know about the other drugs. Looie496 (talk) 00:00, 10 September 2009 (UTC)

I would think that the best drug makers would be the best technicians as opposed to the best engineers or chemists. The reaction pathways are already known, and recipes to achieve those reactions are known. All that remains is to select the best pathway and recipe in terms of safety and purity of yield, then do it properly each time. The incentives for performance are avoiding blowing up your house and avoiding angry dealers whose customers have all been driven insane by the latest batch. A chemist might understand the reaction energetics perfectly but not notice the crud at the rim of the bucket. An engineer might want to scale the process up or use too expensive of gear for the low-volume element. A technician will perfect the recipe.

That's different from drug marketers, many of whom should probably have gone to Harvard so they could do benign things like devastate the world financial system instead. ;) But I'd hire up a really good lab assistant anytime to cook up the best drugs. Franamax (talk) 01:43, 10 September 2009 (UTC)

Drug dealers are dedicated professional physicians who are trained and equipped to deal with medical issues. This documentary video shows the type of skilled after-sales care they give. Cuddlyable3 (talk) 12:23, 10 September 2009 (UTC)

First they poison you with crack, and then they give you medical assistance? 98.234.126.251 (talk) 06:02, 11 September 2009 (UTC)

As an aside, is an adrenaline injection directly to the heart really the correct procedure in case of a cocaine overdose? No, I'm not looking for medical advice, I'm just wondering if they do this for real. After all, moviemakers are pretty notorious for shamelessly mangling the facts. 98.234.126.251 (talk) 06:06, 11 September 2009 (UTC)

Tarantino is a sensationalist semi-amateur hack who has never created anything new. He's the sub-prime mortgage salesman of Hollywood shows. Where is Trovatore, who told me on the other desk that Tolkien is boring? Nay, that movie crap is boring! (Though it's true that Tolkien recycled ancient myths, and Tarantino also recycles familiar movie themes - but Tolkien thought more than 10 minutes ahead). 98.234 as far as I'm aware, direct injection of adrenaline to restart a heart is accepted last-chance technique for non-infarcted heart attack. I'm not sure on exactly how successful it is (though I've seen it done in several movies and it always works there). I'm pretty sure that the miraculously recovered patient doesn't have their makeup and hairdo in perfect shape when they spring back up though. We actually had a mention of this here a while ago, you would need to check the archives. From the last go-round here, I think you need to be pretty precise about where you put the needle, but it seems to be a valid technique.[4] Franamax (talk) 06:22, 11 September 2009 (UTC)