Wikipedia:Reference desk/Archives/Science/2010 July 21

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July 21

A Shocking Experience ?

Can a car battery (12 volt) kill a person ?  Jon Ascton  (talk) 06:41, 21 July 2010 (UTC)

Absolutely, yes it can. The odds of a fatal event will vary greatly depending on the nature of the exposure, the current path through the body, and the availability of life saving efforts. Dragons flight (talk) 06:56, 21 July 2010 (UTC)

You mean, inspite of the fact that it's only 12 volts...

I agree with Dragons flight on the possibility, though you would need to go to very great lengths to kill someone using the car battery alone (except as a blunt object, or by extracting the acid!) . Under normal conditions, the resistance of human skin is sufficient to prevent any harm when handling 12 volts. Dbfirs 07:06, 21 July 2010 (UTC)

Yeah, that's the answer - theoretically it can. But practically there will be problems, like the skin's thickness etc.

A Darwin Award has been made in respect of a death by 9 volt battery. --Tagishsimon (talk) 10:23, 21 July 2010 (UTC)

This is at least the third time we have heard of the Snopes article and the claimed electrocution by ohmmeter. I doubt that it happened. But it is a fair cautionary note, since someone, somewhere might manage to pass enough current from a 9 volt battery through their bodies to stop the heart. If passing current from the 9 volt battery in my ohmmeter stopped my heart, I would be shocked, so to speak. Edison (talk) 19:01, 21 July 2010 (UTC)

If you just shock a vital area of your body, you will be dead; even if the voltage is so low. --Chemicalinterest (talk) 10:57, 21 July 2010 (UTC)

Uh, maybe because voltage has nothing to do with lethality? It's the amperage that kills you. A 12-volt battery can start a V8, a 20,000-volt taser can't. The former has amps, the latter doesn't. Vaguely related: don't put your finger on a spark plug and turn the ignition. It will hurt like hell. No amps, so not lethal, but Christ that stings ZigSaw 13:06, 21 July 2010 (UTC)

This is a silly, oft-repeated oversimplification. Amperage is a good way to measure lethality, but voltage has *everything* to do with how much amperage will be present given a circuit's resistance (even when a human body is that circuit). Given the same resistance (say, a human body) low voltage will *always* result in low amperage, where high voltage will result in high amperage. --144.191.148.3 (talk) 15:15, 21 July 2010 (UTC)

Yes, under normal circumstances, voltage determines whether a source is dangerous, but I have (in my younger and more foolish days) succeeded in giving myself quite a hefty shock (tens of milliamps) from a 12v battery. I won't tell you the method here in case anyone with a weak heart tries it and kills themselves. The probability of death is extremely low, but I cannot afford the law suit. Dbfirs 17:13, 21 July 2010 (UTC)

Actually, stopping the heart with a DC shock won't kill you: it will immediately start up again. AC is much more dangerous because the oscillations can set up a disrupted heart rhythm, leading to fibrillation. The only way a DC shock can produce death is if it has a timing and amplitude precisely balanced to disrupt the heart without fully resetting it. There was a man named George Ralph Mines who did pioneering work on heart rhythms, and apparently died that way as a result of experimenting on himslef, but it isn't clear what voltage levels he used. (See this paper for the story.) Looie496 (talk) 23:08, 21 July 2010 (UTC)

Yes, the body is sensitive to rate of change of current, so one would have to repeatedly connect and disconnect the DC voltage to produce a dangerous effect. Personally, I think the death by ohmmeter article is an urban myth but I presume that George Ralph Mines applied voltages direct to his heart muscle. Dbfirs 06:41, 22 July 2010 (UTC)

Why do we need oxygen?

After reading Alternative_biochemistry, i got wondering, could life exist in other types of atmosphere? The article mentions chlorine but doesn't really elaborate on why. So the question is what is so special about oxygen that we need it and theoretically could this be done by other gases? --90.210.25.177 (talk) 10:59, 21 July 2010 (UTC)

Both oxygen and chlorine are Oxidizers. See Redox for some of the details on what this is. There are lots of other things that can act as oxidizers but oxygen itself works very well, and has a few benefits: it's a very common element (astronomically speaking). When reacted with an even more common element (hydrogen) it produces the universal solvent called water. Chlorine would work as an oxidizer does doesn't do so well with hydrogen. (Hydrogen chloride). The group carbon-oxygen-hydrogen is really quite special in how versatile it is, and simultaneously how common those elements are. Ariel. (talk) 12:26, 21 July 2010 (UTC)

I was checking various hydrogen-oxidizer molecules, and oxygen is really quite the outlier amongst them. Also, in a world with a hydrogen chloride atmosphere or surface, water would be a very powerful corrosive. Ariel. (talk) 12:35, 21 July 2010 (UTC)

Does that mean that independently evolved space-aliens are likely to be oxygen breathers too? 92.29.123.248 (talk) 13:06, 21 July 2010 (UTC)

We don't use oxygen because it produces water. We use oxygen because it can be derived from water. Before the first cyanobacteria started splitting water, life used redox reactions like organosulfur chemistry, oxidiser like nitrates and Fe(III) and so forth. John Riemann Soong (talk) 15:18, 21 July 2010 (UTC)

Hmm, not quite. We use oxygen because you can get a hell of a lot of energy out of oxidizing carbohydrates to CO₂ and water; also because it's there! There's some plausible speculation that water-splitting photosynthesis actually evolved from H₂S-splitting photosynthesis. Physchim62 (talk) 15:50, 21 July 2010 (UTC)

I really don't think that's why we use oxygen. I mean, if life really wanted to make energy-dense compounds, they'd make alkyne motifs all over the place. Much of the water on this planet was carried here by asteroids, probably because most of it boiled off in the initial formation of the Earth. Take the amount of energy not captured by cytochrome complexes in the electron transport chain -- that last jump from complex IV (cytochrome c oxidase) to oxygen is so energetic, the proton gradient it contributes to hardly compensates; most of it is wasted as heat. John Riemann Soong (talk) 16:05, 21 July 2010 (UTC)

Btw, all of this is lifetalk centric to bioorganic chemistry, which if you realise, is really unique to Earth's 1 atm and 1g. A hydrogen sulfide world based on row 3 elements or a mercury world could possibly evolve. Hell, why not a world strongly dependent on a eutectic-based mixture of liquid Fe and specific crystal structures of iron that can only exist at a narrow range of atmospheric pressures and temperatures? The crystal structure is just right to allow for the diffusion of many dislocations and other bulk defects, and atoms travelling in the "solution" can diffuse. Rather than forming cells or membranes, life and "genetic replication" is strongly dependent on crystal growth and chemical networking. The equivalent of cell division would proceed by crystal cleavage, and these microstructures are stabilised by protective network formations and other sophisticated structures based on host-guest chemistry.

There magnetic interactions are just as important as polar bonding, and a "detergent" particle would have both diamagnetic and paramagnetic ends. Rich chemistry can be derived from a mix of Cr(III), Cr(VI), Cu(I),Cu(II), F- and other fun ions. The primary energy source is the planet's ever-churning and changing magnetic field. John Riemann Soong (talk) 15:33, 21 July 2010 (UTC)

The Earth's oxygen was actually created by life, so it couldn't possibly be required for life to exist. (Well, CO2 is required; it isn't clear whether the question means to include this.) Looie496 (talk) 22:57, 21 July 2010 (UTC)

It's true that life started without oxygen, but life as we know it today has probably adapted to living off of oxygen. Therefore, if oxygen were taken away, every animal on Earth right now, with the exception of the most primitive life forms, would probably die. Primitive life forms wouldn't have, but we're not primitive life forms, are we? The Raptor ^{Let's talk}/_{My mistakes; I mean, er, contributions} 23:02, 21 July 2010 (UTC)

Chemistry

Can i please get clear examples of sublimation and its opposite deposition? Is hail an example? why and/or why not? —Preceding unsigned comment added by 74.198.43.60 (talk) 14:56, 21 July 2010 (UTC)

There are a few good examples in Sublimation (phase transition), which you should definitely read if you haven't already. Hail can and does sublimate under the right conditions - ice held at temperatures significantly below its melting point does gradually sublimate to water vapour without melting - but dry ice is probably the easiest and most obvious example to use if you need one. ~ mazca ^talk 15:10, 21 July 2010 (UTC)

(edit conflict) Dry ice , Iodine and ammonium chloride are common examples of things that sublime - see Sublimation (phase transition)

According to Hail " hail forms in cumulonimbus clouds when supercooled water droplets freeze on contact with condensation nuclei" if that's true it's not sublimation since the water is in the form of droplets - which means it is liquid.77.86.76.212 (talk) 15:12, 21 July 2010 (UTC)

Indeed - the formation of hail (and indeed snow) definitely doesn't seem to be desublimation, rather a very fast freezing of liquid water. The appearance of frost on a very cold but non-foggy day is probably the best example of natural desublimation of water that I can think of. The other chemicals mentioned by 77 above are certainly easier examples to use for most things. ~ mazca ^talk 15:19, 21 July 2010 (UTC)

A possible household use is Dye-sublimation printer. Also the ice that forms in a freezer may be from sublimed ice in warmer parts of the freezer. 77.86.76.212 (talk) 15:35, 21 July 2010 (UTC)

You can get desublimation of CO₂ if you use a carbon dioxide fire extinguisher: as the pressurized gas comes out of the nozzle, it rapidly cools (this is the Joule–Thomson effect) and some of it solidifies as a fine white snow (it rapidly resublimes, but the effect is quite impressive). Physchim62 (talk) 15:27, 21 July 2010 (UTC)

Dry ice is the classic, but failing that, frost works too. If you look carefully, You'll notice that frost forms directly on surfaces without a liquid forming first (that's why it's lacy as opposed to being a solid film of ice) - that's deposition: a solid forming directly from a gas (water vapor). The opposite occurs with frost and snow too. In winter you may notice frost disappearing during the day or snowbanks shrinking, even though the temperature stays below freezing. This is because the frost and snow sublime (go directly to water vapor) in the dry air, without melting first. - 174.24.196.51 (talk) 16:46, 21 July 2010 (UTC)

Refrigerant leak?

The inside of both compartments of my refrigerator/freezer smells strongly of some organic solvent. It reminds me of 'model glue'. Does the refrigerant in a modern US refrigerator smell like that? If it is a refrigerant leak, is this generally a repairable problem or it on of those things where repair isn't practical? ike9898 (talk) 15:45, 21 July 2010 (UTC)

Assuming the fridge isn't brand new (in which case it could be the smell of glue used in the construction of it) - it may well be pentane which is a common refidgerant nowadays - in which case your fridge is leaking. It's possible that it could be fixed - but the important thing here would be not to use any naked flames, open all the windows, don't switch on any electrical items then call a fridge engineer from somewhere else and get them to come round - if your fridge is leaking pentane you have a very real explosion hazard.77.86.76.47 (talk) 15:53, 21 July 2010 (UTC)

On the other hand it may be an ozone-friendly fluorocarbon refrigerant with less flammability - it usually says on the fridge instructions or on the back of the fridge what type is used. Fixing a leak involves draining, finding the 'puncture', which may be brazed shut, and then refilling - however the fridge may not have been designed to be taken apart and put back together again (ie glue not screws) - making the repair problematic.77.86.76.47 (talk) 15:57, 21 July 2010 (UTC)

Also if it is leaking the gas may knock you out in sufficient concentrations - most refrigerants are heavier than air - which means they will settle lower down - important if the fridge is not on the ground floor or you have a basement where it can collect - in the worse case a fridge that is leaking is lethal. I would recommend getting it looked at.77.86.76.47 (talk) 16:01, 21 July 2010 (UTC)

Fluorocarbon refrigerants are usually fairly odorless, so yes, this sounds worryingly like a pentane leak. In theory, such a leak can be fixed but, for a domestic refridgerator, replacement may well be a cheaper option. You do need to get it looked at, though, because there is an explosion hazard from the light switch which operates when you open the fridge door... Physchim62 (talk) 16:06, 21 July 2010 (UTC)

Resolved

 – See this section for resolution.

Antibiotics

What kind of effect does a typical seven day course of antibiotics have on organisms that live in the human gut? —Preceding unsigned comment added by 129.67.119.150 (talk) 15:46, 21 July 2010 (UTC)

There are many hundreds of kinds of antibiotic preparations, so your question is too vague to give a definite answer. But "some antibiotics kill bacteria in the gut". You can read our Antibiotic article--I bet there is at least one section relevant to side-effects or somesuch. DMacks (talk) 16:22, 21 July 2010 (UTC)

See also gut flora#Effects of antibiotic use, as well as the individual on specific antibiotics (e.g. amoxicillin or ciprofloxacin). TenOfAllTrades(talk) 19:19, 21 July 2010 (UTC)

What do you call this sort of cytoplasmic channel?

Please help! Thanks, so I can search for it in the literature. I was observing a bunch of lung cancer cells (epithelial) under DIC microscopy. These cells had an initial connection of two tiny strands (nanotubules?) that later grew into an entire cytoplasmic channel. I saw a gold nanorod (25x73 nm) being transported across one of the stands as well as other vesicles crowding into the newly-formed channel. At the same time, I saw another cytoplasmic channel between the same cells being disassembled back into tububles; in time the tubules were even broken. The channel that formed remained strong though. What do you call these channels and tubules?

The particle being transported across the strand appeared not to be by free diffusion, but by actual binding (it stopped its flashy rotation behaviour while on the strand). I'm not sure if this is an actual microtubule or a complex of other types of polymers. Help! John Riemann Soong (talk) 16:38, 21 July 2010 (UTC)

Microtubules are part of the cytoskeleton and not actual "tubes" through which things are transported. Think of them as cables that motor proteins use to transport things around inside of a cell. There is no cellular component called a "nanotubule". You might be seeing a connection between two cellular protrusions, like filopodia, or the remnants of the cell membrane that sometimes happen after a cell divides but the daughter cells remain connected by retraction fibers (redlink? hmmm... might have to fix that). How close together were the two cells? Are your nanorods intracellular or extracellular? Can you post a photo? --- Medical geneticist (talk) 17:00, 21 July 2010 (UTC)

The cells (from memory) were separated by a distance about 2-5 micrometres apart. The nanorods were endocytosed and definitely intracellular. I was trying to witness an exocytosis event but the rods travelled across these strands instead. I don't know if the strands I saw were cables by which motor proteins were attached to, or actual very narrow channels. In time, membrane surrounded these strands and expanded to something like 10-20 times the strands' width (the strands were still the same width though). I took videos and photos which I may post soon, when I retrieve it from the lab hard disk. John Riemann Soong (talk) 17:18, 21 July 2010 (UTC)

How about membrane nanotubes? Maybe take a look at some figures in the references given in the article and see if they are similar. Smartse (talk) 20:18, 21 July 2010 (UTC)

I stand corrected! I would have used the term cytoneme but if people are calling those things "membrane nanotubes" these days it shows how long it's been since I learned cell biology! Back to the question... you probably are seeing some type of membranous tether between the cells. These things are sometimes hollow but often contain some type of structured cytoskeleton, usually actin and sometimes including microtubules, to allow for transport. When you see them expanding, I'd guess that's because they are filling up with cytoplasm. For what reason, I can't say. Still, sounds very interesting. --- Medical geneticist (talk) 21:56, 21 July 2010 (UTC)

Survival benefits of scratching

Deleted See July 19 for the same topic

Sheep breeding season

When exactly do sheep on farms (in temperate climates) tend to give birth? The domestic sheep article just says "in the autumn", which is not very specific. 86.143.231.207 (talk) 17:24, 21 July 2010 (UTC)

No, conception (tupping) is in the autumn. Lambs are born in spring. Dbfirs 18:07, 21 July 2010 (UTC)

Early spring, or technically late winter if memory serves. I think March is the most common month, but it might depend on where you are. Temperate climate is pretty broad. Googlemeister (talk) 19:48, 21 July 2010 (UTC)

Yes, where I live in the Pennines, sheep naturally lamb in April, but, for commercial reasons, many farmers (especially in milder climates) bring tupping forward to late summer and have lambs born indoors in January. Dbfirs 21:01, 21 July 2010 (UTC)

Note, however, that this technique is not known to have been practiced in 1st-century Judea :-). 87.81.230.195 (talk) 22:32, 21 July 2010 (UTC)

It is indeed thought that the true birthday of Jesus, assuming the biblical accounts about the shepherds are accurate, might well have been in the spring. The Romans choose the winter solstice as the time to celebrate Jesus' birth, as they already had spring covered by Easter. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:04, 22 July 2010 (UTC)

Wind Turbines on Cars

I was in the car with a couple of friends at the weekend, and one of them suggested putting a wind turbine on the roof in order to generate energy to subsidise the energy use of the car. I said that the turbine would create drag and would slow the car down, and so more fuel would need to be used to drive the same distance; meaning that net energy use would go up, and not down as desired. Even if the turbine converted energy perfectly, and without waste, the best that could be hoped for would be a constant net energy use.

One of my friends then suggested a turbine might be put behind the radiator grill of the car. Without the turbine, the air entering the radiator grill would be pushing against the car and impeding the car's progress. Putting a turbine behind the radiator grill would turn some of the stopping force of the wind into energy that could be used to propel the car.

Would the wind turbine still create drag, even though it was hidden away behind the radiator grill? The wind entering the radiator grill would otherwise just push against the car and slow the car. Would the turbine absorb some of this stopping energy, making the car slow less quickly, whilst at the same time generate energy to be used by the car? Are there any more comments and observations that you would like to make? I would really appreciate some input on this. •• Fly by Night (talk) 18:09, 21 July 2010 (UTC)

If I am not mistaken, the turbine would really not turn much, as the wind would pass through the turbine and stop on whatever is behind it, building up pressure, and trying to force itself back out. I could be wrong about how the turbine would behave, as I have never tried such an experiment, but laws of physics will tell you that you are not going to gain any energy by doing that. There are some things you can do to lose less energy, such as in a hybrid car (storing the stopping energy), but I don't think a wind turbine would help do anything on the car, except make it less efficient and heavier. Falconus^{p t c} 18:17, 21 July 2010 (UTC)

The air would flow past the turbine and into the radiator proper; where it would be used to cool the engine. In fact, some cars even have a fan on the other side of the radiator, powered by the fan belt, which pulls the air through the radiator. So I don't think there would be any build-up of pressure. Having said that, if there is a constant stream of air passing through the grill and then the radiator, assisted by the a fan then there's steady stream of air. That wouldn't stop the car as I thought. And putting a turbine in that air would again cause drag and hence slow the car... Does that sound right? •• Fly by Night (talk) 18:53, 21 July 2010 (UTC)

The Mitsubishi i-MiEV Sport concept car had wind turbines behind the grille. I don't know whether the production i-MiEV does or not. Adding wind turbines can increase overall efficiency; this doesn't violate any conservation laws. There was a ref desk thread on this subject recently: 2010 June 11#Windmill on a car ?. -- BenRG (talk) 19:01, 21 July 2010 (UTC)

(after edit conflict) ::Yes, I agree with Falconus that this is not a practical option. When turbines were last discussed here (thanks for the link, Ben), it was suggested that, in theory, a wind turbine mounted on a car could generate electricity from the wind without (in theory) needing to draw energy from the engine of the car. The problem seems to be, as you correctly stated, that drag on the structure would drain a greater amount of energy than would be gained. Your suggestion might work with some clever aerodynamic design to prevent back-pressure, but then the energy to drive the turbine could come only from a true headwind (or from the car engine). It's a clever idea, but the amount of energy to be gained is probably not worth the effort. Car aerodynamics are fairly complex, and I'm not sure how the change in airflow would affect drag. If the air has to flow through for cooling anyway, and energy can be harvested as it passes, then this is gain even if the energy does come from the engine in the first place. Dbfirs 19:18, 21 July 2010 (UTC)

This is not the same thing at all, but still a remarkable piece of engineering. It is a wind-powered car that can travel downwind faster than the wind is blowing. Enjoy! TenOfAllTrades(talk) 19:25, 21 July 2010 (UTC)

(ec, five times!) BenRG, this is not correct. It does cost energy. The turbine acts as resistance to the air. Instead of just passing through, the air is blocked. This resistance costs energy. However, if your design of the car is such that you have friction resistance anyway, and switch it to turbine resistance then that is a benefit - but in that case you would be better off just removing the friction resistance and leaving out the turbine. Ariel. (talk) 19:26, 21 July 2010 (UTC)

Perhaps a small turbine strategically placed over the radiator, facing down and properly shielded from the wind caused by the car's motion would be able to provide benefit from the heat rising off of the radiator. Googlemeister (talk) 19:47, 21 July 2010 (UTC)

The car is in motion, so the air would not rise. It would be swept backwards into the engine. •• Fly by Night (talk) 19:51, 21 July 2010 (UTC)

Ariel, nothing that you said contradicts anything that I said. -- BenRG (talk) 23:57, 21 July 2010 (UTC)

You said "Adding wind turbines can increase overall efficiency; this doesn't violate any conservation laws." But that's not correct, adding a turbine will add friction. Unless you mean to harvest energy from external wind, but if so it wasn't obvious to me that that is what you meant. Ariel. (talk) 02:38, 22 July 2010 (UTC)

If the turbine is directly in the flow of air then it will create drag. It will push back on the air that pushes it. Also, if the airflow is used to cool the radiator (and in turn the engine) then surely by putting a turbine in the airflow you will decrease the wind speed and so decrease the cooling ability of the air. That means that the engine would run at higher temperatures. •• Fly by Night (talk) 19:51, 21 July 2010 (UTC)

Land yachts (and especially ice yachts) can got several times the wind speed, by sailing at about 45degrees into to apparent wind . 62.56.49.134 (talk) 20:21, 21 July 2010 (UTC)

Yes, this, and TenOfAllTrades' link, prove that energy can be harvested from the wind whilst travelling, but there are problems implementing this effectively in a motor vehicle. Efforts at present go into reducing drag and improving the efficiency of engines, where there are much larger gains to be made. Dbfirs 20:47, 21 July 2010 (UTC)

Follow up refrigerant leak question

I seem to have a refrigerant leak in refrigerator/freezer. Both compartments have a strong solvent smell. I have a service tech coming in the morning.

So now for the question... In the meantime, is the food stored in this refrigerator safe to eat? There is no liquid residue anywhere in either compartment. I'm just concerned about whether the food or beverages would have absorbed the vapor in concentrations great enough to matter. Would absorption be greater for fatty foods? ike9898 (talk) 19:59, 21 July 2010 (UTC)

Update: I spoke with the manufacturer's tech support. They said the refrigerant in my model is freon, and that freon doesn't smell like that. They didn't think anything in the refrigerator should cause that smell. ike9898 (talk) 20:28, 21 July 2010 (UTC)

Perhaps it's rotten meat? Or spoiled milk? Is there anything like that in the refrigerator? The Raptor ^{Let's talk}/_{My mistakes; I mean, er, contributions} 20:44, 21 July 2010 (UTC)

Mmmmh. Could it be ripe fruit and veg - the cold temperatures mean than only the "high notes" of smells are volatile - these compounds are typically solvent like in smell and form eg small amounts of butane, butanal, acetaldehyde, ethylacetate.

Fridges do smell for this reason, even when cheese is removed - but I wouldn't say it is a strong smell.

Q. Is the smell 'alarming' - I'm not aware of this - but it seems likely/sensible for manufacturers to put a smelly compound in the freon in case of a leak.. 77.86.76.47 (talk) 20:48, 21 July 2010 (UTC)

When some plastics overheat, they can give off strange odours. Is anything getting hot? Dbfirs 20:49, 21 July 2010 (UTC)

A speculative suggestion, but partially consumed fruit juices (which on opening can be inoculated by wild yeast from the air much as in Lambic beer brewing) can if left long enough ferment and develop a noticeable alcoholic smell - it's happened in my own fridge! Could this be the source? 87.81.230.195 (talk) 22:28, 21 July 2010 (UTC)

To answer the original question, I don't think there would be any undue risk from eating the food in the fridge unless the food itself was smelly. If it a Freon leak, then Freon is notoriously non-toxic to mammals (except when it gets to the ozone layer, but that is not most people's definition of toxicity). In the case here, I would simply use my general judgement as to what to eat out of my fridge – if it looks or smells bad, don't eat it; if it looks and smells OK, eat it! Physchim62 (talk) 00:39, 22 July 2010 (UTC)

"Strong solvent smell" - could be ripe bananas. Have you tried removing everything from the fridge, cleaning it, and seeing if it still smells? 92.28.250.141 (talk) 10:00, 22 July 2010 (UTC)

Doesn't storing bananas in the fridge ruin them? Googlemeister (talk) 14:06, 22 July 2010 (UTC)

It makes the skin turn black and may negatively affect the texture but they definitely last longer (i.e. are edible/usable for longer) so it depends on what you mean by 'ruins' Nil Einne (talk) 15:16, 22 July 2010 (UTC)

Resolved

 – Original poster, ike9898 (talk)

I find this hard to believe, because it really, really didn't smell like rotten food, but it was. Some produce in the crisper drawer. The smell was actually strongest in the freezer; I suspect the freezer was acting as a condenser, and accumulating the volatiles. Thanks for all your help. ike9898 (talk) 14:28, 22 July 2010 (UTC)

For our own future reference (and current curiosity), are you able and willing to specify what the 'produce' was? 87.81.230.195 (talk) 17:04, 22 July 2010 (UTC)

I think it was carrots and celery (don't know if one or both were bad, we threw it all out). They were bad to the point that nasty liquid had drained off them and collected in the drawer. The funniest thing is that just smelling the drawer, the smell wasn't that bad. I hypothesize that the volatiles were getting concentrated in the freezer. ike9898 (talk) 17:43, 22 July 2010 (UTC)

Whole onions can smell like that when they start going soft. 92.29.117.211 (talk) 20:28, 22 July 2010 (UTC)

Avro Vulcan

What is the carbon footprint of the Avro Vulcan?

Apart from the technical answer, can you please translate that into what that equates to compared to say, the Ford Fiesta, a London bus, Intercity 125, x flights to New York on a 747 or something we can more easily visualise!

Thanks. —Preceding unsigned comment added by EnglishNomad (talk • contribs) 20:47, 21 July 2010 (UTC)

It's not possible to answer your question as written. Are you asking about the fuel efficiency of this vs other vehicles? They hold different numbers of people, so do you want to take that into account? Why would you specify "to New York" - what different does the destination make? And you don't give the departure location (not that it matters if you just want fuel per mile - or do you?) All liquid hydrocarbon fuels generate more or less the same carbon dioxide, so just check the total fuel divided by maximum range for each of those. But it depends on the speed, basically this question is impossible to answer. Try: Fuel efficiency in transportation - it might have the answer to your question. Ariel. (talk) 20:56, 21 July 2010 (UTC)

An exact figure is truly impossible to estimate because we can't know how much went into manufacturing, servicing, etc. But simple fuel loads are easy - the thing carries 40,000 liters of fuel and it has a range of about 4,000km - so 0.1km/liter. A MkV Diesel Ford Fiesta does 30km/liter - so on a very rough estimate - the Vulcan is 300 times worse. SteveBaker (talk) 21:09, 21 July 2010 (UTC)

Keep in mind that unlike a car, an aircraft's fuel consumption rate can vary by orders of magnitude during a single flight. This is because of huge variation in the level of throttling, the immense change in mass as fuel is consumed (or combat payloads are deployed), climbing vs. cruising, and so on. Our article on jet aircraft range has some equations to calculate fuel consumption for an aircraft. Automobiles also have a "time-variation" in fuel consumption / mileage-per-gallon; but it usually doesn't vary by a factor of 100x over the course of a single drive outing, even accounting for things like acceleration and hills. Nimur (talk) 22:10, 21 July 2010 (UTC)

True, but a car's fuel consumption does vary by a factor of at least ten. (original research on local hills) Dbfirs 06:29, 22 July 2010 (UTC)

It has 4 rolls royce olympus engines - which have a fuel consumption to thrust ratio (see Thrust specific fuel consumption) of ~1.3 (imperial) - thrust is ~10,000ftlb each making the fuel consumption 40,000x1.3 = 52,000 lb/hr - in metric that's ~6.6kg/s of fuel in flight (2.2 pounds per kg, 3600 seconds per hour). Jet fuel has a calorific value of ~47MJ/kg (see Fuel_efficiency#Energy_content_of_fuel). So the machine is using 47x6.6 = 310MJ/s or 310MW (somebody should check these figures for mistakes)

That's approximately 100 Intercity 125's or 26 Eurostars , or 100,000 kettles. 77.86.76.47 (talk) 21:18, 21 July 2010 (UTC)

Assuming the thing does about 900km/hr at the above thrust (which is 0.25km/s) it does 0.25/310 = 0.0008km/MJ (or 1240MJ/km), but the crew is 5 so the figure for Megajoules per passenger kilometer is 1240/5 = 249 (which is about 100 times worse than using a bus) 77.86.76.47 (talk) 21:38, 21 July 2010 (UTC)

The Vulcan was not originally designed to be a passenger vehicle: if the question relates to the model of aircraft in general, one might wish to factor in the relative payloads of the vehicles being compared - a freight aircraft would arguably the 'fairest' comparison. On the other hand, the individual remaining airworthy Vulcan is used only for display and not to carry payloads (certainly not the specific ones it was designed for!) so perhaps comparison to passenger vehicles is more valid. Admittedly EnglishNomad did not actually ask for these nuances of interpretation. 87.81.230.195 (talk) 22:22, 21 July 2010 (UTC)

I multiplied force x velocity to determine power. The engines deliver around 13,000 lbf at around 925 km/hr, so 4 * 76 kN * 925 km/hr is around 100 megawatts of kinetic power. Assuming a ballpark thermodynamic efficiency of ~ 30%, 77.86's numbers seem to check out. Another way to look at it, 300 megawatts is about the instantaneous electricity consumption of a mid-sized city; so flying one combat bombing-run sortie of an Avro Vulcan to wipe one city off the map is tantamount to adding another city to the energy-economy, based on the aircraft's fuel-consumption alone. I suppose these things even out? Actually, on further reading, the Vulcan could carry two air-launched cruise-missiles, one under each wing pylon; so as usual, nuclear warfare does actually yield a net loss. Nimur (talk) 22:14, 21 July 2010 (UTC)

Colour-in 3D chick embryogenesis models/pictures?

I'm trying to study (as in reading, rather than experimenting) expression of a gene during in chick embryogenesis but it's difficult to keep a mental hold on the movements of the expression patterns. What would really aid me would be some 3D computer models of chick embryogenesis (HH stages in particular) to which I could colour in the locations of gene expression. 2D would be better than nothing, but would require two pictures to represent 3D patterns. Such blank pictures probably don't exist on the web for free, but I figured it's worth a shot. ----Seans Potato Business 21:01, 21 July 2010 (UTC)

Birds

is peanut butter bad for birds to eat? some books say it kills them and others say its a good treat for them.--Horseluv10 21:22, 21 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

I would expect it depends on which birds you give it to. Different birds have different diets. --Tango (talk) 21:44, 21 July 2010 (UTC)

see http://birding.about.com/od/birdfeeders/tp/birdfeedingmyths.htm --Digrpat (talk) 21:48, 21 July 2010 (UTC)

Considering how much many birds love peanuts, I have a hard time believing they'd die from peanut butter without a really good reference. Matt Deres (talk) 21:58, 21 July 2010 (UTC)

My understanding with peanut butter is that it's lacking in some amino acids, so if an animal feeds on it exclusively they will suffer from a form of Kwashiorkor. Ariel. (talk) 22:36, 21 July 2010 (UTC)

Do you have any reason to suspect that would affect birds, though? - not all animals need to intake the same amino acids (see essential amino acid); organisms may synthesize different amino acids internally. Many birds also seem to get by on a whole variety of seemingly narrow diets (pine cone seeds, sunflower seeds, etc.). I'm not saying you're wrong, I'm just saying that my understanding of bird diet would make me suspicious of the various claims in this thread (peanut butter is bad, an exclusive diet of peanuts/peanut butter would fail to provide all a bird's required amino acids) without a really good reference. If a crossbill can be so intimately tied to a particular species of pine seed that it suffers when it has to switch to a different species in times of hardship, that makes me think that birds don't generally need the same kind of variety of diet that people do. Matt Deres (talk) 01:01, 22 July 2010 (UTC)

Your average crow, for example, eats rotting carcasses on the road, so I doubt peanut butter would bother it much, except it might be kinda gooey. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:00, 22 July 2010 (UTC)

people say that it can clog their digestive system and kill them, that's why i was asking--Horseluv10 20:04, 22 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

Peanut butter is only a danger to birds because it's so sticky - it creates a choking hazard if you just dump a big glob of it out for the birds. If you cut it with with something to make it a little more liquid or offer it (in cold weather) is small bits it shouldn't be a problem. probably best to mix it with other materials - like seeds - as well, just for nutritional balance. --Ludwigs2 03:01, 23 July 2010 (UTC)

I heard that chocolate is toxic to birds. If you put some out, will they eat it? —Preceding unsigned comment added by FoulEmission (talk • contribs) 02:31, 23 July 2010 (UTC)

Our article on theobromine poisoning says that parrots are very susceptible to chocolate poisoning. Because they're often kept indoors as pets, they're probably more likely to come in contact with it... I would not leave chocolate out for birds to eat; it's likely just as toxic to finches and sparrows. In my house, chocolate doesn't get left lying around for long in any case... Matt Deres (talk) 13:19, 23 July 2010 (UTC)

Yosemite

hey all I am going to yosimite tomorrow and I want to know what the chance of me meeting/being attacked by a wild animal like a cougar or bear is and if there is anything I might do that would increase and anything that might decrease my chance of the same. Thnx. 76.199.166.85 (talk) 23:30, 21 July 2010 (UTC)

If you smear yourself with peanut butter and barbecue sauce and go walking naked through the woods at night, you'll increase your chances of being attacked by a bear. Basically the rule is, don't wave food in front of bears and you'll be okay. There are no other animals worth thinking about there. Looie496 (talk) 23:35, 21 July 2010 (UTC)

Here are Safety Tips, particularly as they pertain to bears and food storage. In truth, you have a greater chance of harm by falling off one of the waterfalls than by animal-attack. But, if you don't take proper precautions, especially if you are out of the valley, bears can be a real threat. Nimur (talk) 00:33, 22 July 2010 (UTC)

They are a threat to your food. Yosemite bears don't attack people unless the people try to take food away from them. Looie496 (talk) 00:52, 22 July 2010 (UTC)

(But they might tear your car door off). Nimur (talk) 20:03, 22 July 2010 (UTC)

Nimur, thanks for the image; I've uploaded it as File:Bear damage to car door.jpg and added it to Bear attacks. Nyttend (talk) 00:32, 25 July 2010 (UTC)

Excellent addition. You mis-labeled it as a Brown Bear attack, but it was a Black Bear attack in Yosemite. I corrected it on the image page and the article. For more information on brown vs. black bears in Yosemite: Bears in Yosemite. Nimur (talk) 23:47, 25 July 2010 (UTC)

Don't mess with any bear cubs (I mean don't get anywhere near them), or try to get a photo of you hugging the bear along with the above mentioned food advice and you should be ok. Googlemeister (talk) 13:22, 22 July 2010 (UTC)

The time-honored theory would be to bring along a friend that you're confident cannot run as fast as you can. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:58, 22 July 2010 (UTC)