Wikipedia:Reference desk/Archives/Science/2010 June 12

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June 12

Atomic mass unit

Why are the values for 1 amu different if you use 1/12 the mass of a carbon-12 atom instead of 1/16 the mass of an oxygen-16 atom? The former has 12 nuclear particles of equal mass, and the latter has 16 nuclear particles of equal mass to each other and to the particles in a carbon-12 atom. --75.25.103.109 (talk) 00:41, 12 June 2010 (UTC)

See Binding energy#Mass deficit. The different nuclei have different binding energies, so different mass deficits. It's also worth nothing that protons and neutrons don't actually have the same mass (although it is very close). That doesn't affect your example, since they each have half protons and half neutrons, so the average mass is the same, but if you are talking about heavier nuclei (which need disproportionately more neutrons to be stable) it becomes an important factor. --Tango (talk) 00:48, 12 June 2010 (UTC)

Tornado recurrence rate

I remember reading this in a book at some point, but I have never been able to find it since. What is the recurrence rate of a tornado striking any given point in the tornado-active areas of the United States Great Plains, say in Kansas or Oklahoma? The statistic I remember reading was something on the order of once every *insert number above 500 here* years, but I have never been able to find the statistic again. The context I remember it being used in was to explain how very rare and against all odds such events as Codell, Kansas's (struck by tornadoes on May 20th of three consecutive years) or Mulhall, Oklahoma's (struck by two violent tornadoes within a 2 hour time frame) tornado events are. Ks0stm ^(T•C•G) 02:47, 12 June 2010 (UTC)

This site says "Even in tornado alley, a twister hits a given square mile only once every 700 years" but it's not well referenced. Regards, --—Cyclonenim | Chat  11:19, 12 June 2010 (UTC)

Being hit repeatedly in a short time period isn't too uncommon: a single storm may generate multiple tornadoes, which will tend to have similar tracks. --Carnildo (talk) 00:00, 17 June 2010 (UTC)

Female Survival

Ok, I know this will sound incredibly stupid, but I'm going to ask it anyway. If a woman was stranded somewhere without food or water, could she drink milk from her own breasts to survive? Or would the lack of nutrients cause the milk to lack any nutritional benefits? Could the energy and nutrients be recycled through the body< of would it be lost? If so, how quickly? Again, I know this sounds incredibly stupid, but I realize that I have been wondering about this for quite a while now. Thanks for the help, and please don't think I'm some kind of weirdo for asking this! Stripey the crab (talk) 03:10, 12 June 2010 (UTC)

Of course not! It takes energy to produce milk - and by the basic laws of thermodynamics, it must cost more energy to make than can possibly be gained by consuming it! SteveBaker (talk) 03:40, 12 June 2010 (UTC)

However, she might be advised to read up on urophagia before getting stranded.--Shantavira|^{feed me} 06:23, 12 June 2010 (UTC)

Conservation of energy 82.43.89.11 (talk) 11:24, 12 June 2010 (UTC)

Yes, she could, but the longer she lived on the less nutrional it would be until she died of starvation. You could survive a while on your own scabs, excrement, urine etc. Only a bit longer than going without food but it would prolong life nonetheless.--178.167.206.65 (talk) 13:41, 12 June 2010 (UTC)

But would there be any advantage to drinking your own milk? If you stop breast feeding, you'll soon stop lactating and I would imagine any milk left would be reabsorbed. --Tango (talk) 17:06, 12 June 2010 (UTC)

A transverse wave

Visit [1] and go to question 12. These are my answers for part a:
Frequency: 10 Hz, 10 Hz
Amplitude: 0.2m, 0.15m (or perhaps 0.14m)
Wavelength: 2m, 1m
Speed of wave: 20m/s, 10m/s

But now I'm stuck on question b. How do you do it?--220.253.96.217 (talk) 04:10, 12 June 2010 (UTC)

From your answers to part (a), you can determine that the transmitted pulse (travelling to the right on the heavy string) will have a smaller amplitude than the original pulse. I would think that the reflected pulse (travelling to the left on the light string) would have an even smaller amplitude (most of the energy will go into the transmitted pulse) but it will be travelling twice as fast as the transmitted pulse. If you take a snapshot at, say, 0.1 s after the original pulse arrives at the junction, then the transmitted pulse will have travelled 1m to the right, and the reflected pulse will have travelled 2m to the left. You are only expected to sketch the appearance of the two pulses, and part (b) is only worth 3 marks as opposed to 6 marks for the quantative answers in part (a), so you don't need to very precise. Gandalf61 (talk) 09:35, 12 June 2010 (UTC)

The answer can be found here [2] by the way, but what I want is not the answer itself, but how you work the answer out.--220.253.96.217 (talk) 11:12, 12 June 2010 (UTC)

Computer components from petrochemicals

Which computer components (if any) are made from which materials derived from petroleum? -- Wavelength (talk) 07:17, 12 June 2010 (UTC)

The Integrated circuit encapsulation, any Insulator (electrical), epoxy in the Printed circuit board, engineering plastics in the DVD drive, external parts eg keyboard keys.77.86.125.56 (talk) 08:10, 12 June 2010 (UTC)

And lest we forget all the electricity needed to build the components, and where that comes from. Regards, --—Cyclonenim | Chat  11:17, 12 June 2010 (UTC)

It is unlikely that the electricity to manufacture electronic components comes from petroleum (or even natural gas). See the charts in electricity generation. For the United States, half the energy for electricity comes from coal, natural gas is nearly a quarter, almost all of what is left is nuclear; and the remainder is a tiny sliver of renewables, bio-fuels, hydro-energy, and geothermal. A tiny (minuscule) fraction of electricity comes from petroleum. An even smaller fraction comes from solar production. Furthermore, most electronics components are manufactured overseas (specifically, China, where coal is overwhelmingly the largest source of the energy for electricity). Very little petroleum is used to provide energy during the manufacture of those electronic components. Nonetheless, petroleum is used in massive scales to transport the materials - and transportation is the single largest energy-consuming sector (if you can call it a single sector). Nimur (talk) 16:35, 12 June 2010 (UTC)

Thank you all for your answers. Although I was hoping for more detailed information, I appreciate the information provided.
-- Wavelength (talk) 15:06, 13 June 2010 (UTC)

How about the following: FR-4, Integrated circuit packaging, Integrated circuit encapsulation, Potting (electronics), Resin dispensing? In the old days, circuits were packed in ceramic; nowadays, plastics, epoxies, silicone derivatives, and resins are more common; silicone is made from Dimethyldichlorosilane, made from Chloromethane, made from methanol, which is made in industrial scales from natural gas (methane). Epoxies are often made from epichlorohydrin, which can be made from heavy asphaltenes, paraffins, and petroleum residues. Similarly, if you click through the "production" or "synthesis" sections of most of the other constituents, and trace back far enough, you'll find the eventual source chemicals. Most of the electronics are not at all derived from petroleum or petrochemicals - but the packaging (without which the electronics would be useless) are petrochemical-derivatives. Furthermore, photoresist (a critical step in modern VLSI electronics) is also a petrochemical derivative. Hopefully this is a little more specific for at least some sub-areas of the electronic components - your original question covers so broad a topic that it is difficult to be both complete and specific. Nimur (talk) 16:21, 13 June 2010 (UTC)

Thank you for the additional information. -- Wavelength (talk) 14:30, 14 June 2010 (UTC)

heat

my power went out today when it came back on my gas central heat only pumps out cold air not hot air. i dont have any AC. how do i fix this ? its like my thermostat isint communicating with my heater properly. —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 08:12, 12 June 2010 (UTC)

It could be several problems. It could be a defective safety on your furnace to prevent keeping the flame on when no blower is on. It could be your thermostat, but that is more unlikely with battery powered thermostats. --Chemicalinterest (talk) 10:59, 12 June 2010 (UTC)

could the power going out ruined or damaged the thermostat? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 11:34, 12 June 2010 (UTC)

and whats weird it has a space for a battery but i havent used one in years. when the power came back on the thermostat wouldent even turn on and i had to put in batteries to even make the display show up. why is that? it ran for years fine on house power. in the past when the power went out it came back on no problem. —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 11:42, 12 June 2010 (UTC)

If your system is anything like my gas-fired hot water central heating system, Alexsmith44, then if your heater is not heating the air the burners may not be lighting, which suggests that the pilot light that ignites them may be out; this pilot light usually maintains a high temperature in a thermocouple which, if not hot, prevents gas from flowing to the pilot light and the main burners in order to prevent a large escape of gas blowing up your house. (Lighting the pilot usually requires you to manually over-ride the pilot light cutoff until the thermocouple is up to temperature.) Lighting the pilot usually requires either piezolectric spark ignition (usually achieved mechanically by pushing a button) or a spark derived from a battery or the mains electrical supply.

Is your pilot light lit? If not, the power cut may have caused it to go off for safety reasons, and you need to relight it, which will require the relevant components to be in good shape and the exact procedure in your appliance manual to be followed. If you are in any doubt about any of this (for example, if you don't have the manual) then call a qualified gas appliance engineer - gas appliances are too dangerous to be tinkered with by someone who doesn't know what they're doing.

If none of this is relevant, and/or you do know what you're doing (though if so why are you asking here?) then you have my apologies, but please don't risk blowing up yourself and your building! 87.81.230.195 (talk) 18:09, 12 June 2010 (UTC)

can anyone explain why when the power came back on the thermostat wouldent even turn on and i had to put in batteries to even make the display show up.

There are almost certainly too many different configurations of this general sort of system for anyone to have a chance of diagnosing such problems unless you say exactly what make and model your system is (and even then there would be no guarantee that anyone answering here could do so).

One thing I should add to my previous post: if your system includes a pilot-light-heated thermocouple, it might have failed when or after the system went down, or when you tried to restart it. Such thermocouples are probably the most failure-prone component of gas-fired heating systems - my own boiler's thermocouple failed at least 3 times during a 20-year period.

Even if anyone answering here can correctly guess the cause of your problem, you're not going to be able to be sure they're right, you're probably not going to be able to fix it, and you're going to run the risk of causing more damage to the system or yourself if you try but get it wrong, so you're going to have to call in a qualified engineer who will be able to make a sure diagnosis and carry out a safe repair/replacement. He/she is the person to ask. 87.81.230.195 (talk) 04:24, 13 June 2010 (UTC)

Some thermostats run on electricity created from the heat of the pilot (and so don't need a mains or even a battery connection). But it won't work without a heat source. Rmhermen (talk) 00:27, 14 June 2010 (UTC)

I hope the OP didn't live here! 87.81.230.195 (talk) 03:28, 14 June 2010 (UTC)

BP gulf oil issue: Geology question

Forgive my ignorance on the matter, but I was just curious about something: the world is focusing on the oceans and shores and flora/fauna, etc etc (and rightly so). But emptying at an estimated rate of 40,000 gallons a day, what's happening to the pocket where the oil is originally coming from? At what point would the pressure/weight of the ocean collapse the oil pocket? What would be the extent of the damage this incurred, or would the "earth" not even notice (like earthquake or tsunami, etc)? – Kerαunoςcopia^◁_galaxies 10:08, 12 June 2010 (UTC)

In most cases extracting oil or gas from a reservoir has relatively minor effects, as the hydrocarbon in the rock pores is replaced by water. The thing to remember is that we're not talking about a hole in the ground filled with oil, but a rock with maybe 20% porosity. Mikenorton (talk) 10:22, 12 June 2010 (UTC)

Just to expand a little on my response above, as the oil comes out, the pressure in the reservoir will reduce, something known as depletion, and this will lead to some compaction of the reservoir unit from the pressure of the overlying rock. In some cases this has led to induced seismicity on a small-scale [3] and minor seafloor subsidence [4]. Mikenorton (talk) 13:30, 12 June 2010 (UTC)

The rock is like an oil-filled sponge, so there is no big underground cave that is emptied. That said, normal oil production could make the seafloor sink gradually as oil is emptied. From the top of my head I know of an offshore oil rig that sunk by 20 metres over a couple of decades, because the oil reservoar below it was compacting. If you'r looking for geological catastrophes caused by the oil industry, the Lusi mud volcano is a much more dramatic example. EverGreg (talk) 12:11, 14 June 2010 (UTC)

Great! Thank you for the responses! – Kerαunoςcopia^◁_galaxies 18:25, 16 June 2010 (UTC)

Cats and mirrors

A follow-up to the discussion above at Wikipedia:Reference_desk/Science#Sentience.2Fconsciousness, my cat will watch me reflected in dark glass (doors, windows, all at night, reflecting the lighted interior well), and if I walk up to him quietly and kneel down, he'll watch me, then turn around and come to me. He's also waited at the door to be let out, but instead of meowing at me me, he'll watch me in the reflection, and when I arrive, look up at me again. He's obviously aware that he's the "little guy" in the reflection and I'm the taller one lol. Um, I guess my silly question would be, what does this prove? – Kerαunoςcopia^◁_galaxies 10:15, 12 June 2010 (UTC)

it proves you have an enviable amount of free time! 92.230.234.180 (talk) 10:37, 12 June 2010 (UTC)

It means animals can understand mirrors. --Chemicalinterest (talk) 10:57, 12 June 2010 (UTC)

No, it means cats (not all animals) are aware of their own reflection and potentially other things in the reflection. Cats are creatures of habit, if they see a reflection every time before the door opens, they'll associate that reflection with an opening door. They're also acutely aware of their surroundings, just because he/she looks up at you as you arrive doesn't mean they necessarily saw you in the mirror. Regards, --—Cyclonenim | Chat  11:14, 12 June 2010 (UTC)

I don't see why any part of the OP's story means that cats are aware of their own reflection. The story was entirely about identifying a reflected human shape as a human (and the assumption about awareness of "the little guy" came out of the blue). The cat doesn't react to its own reflection as it might do to a real cat on the other side of the glass, but that doesn't indicate awareness, only some basic filtering out from the cat's attention of objects that move in sync with the cat's muscle movements. (There might be a name for this, I forget - proprioception?) 213.122.19.215 (talk) 11:26, 12 June 2010 (UTC)

How does anyone know that cats are not aware of their own reflection?--178.167.206.65 (talk) 13:44, 12 June 2010 (UTC)

See Mirror test. Deor (talk) 13:51, 12 June 2010 (UTC)

The problem with the mirror test is that it is incapable of distinguishing between self-awareness (in this sense, the ability to recognize that the object in the mirror is a reflection of the self) and self-consciousness (an ability to compare the reflection against an internal self-representation to note differences). Animals who fail the mirror test (such as cats and dogs) may in fact be aware that the mirror is reflecting them, but may not recognize that the test dye that the researcher placed on them is something unusual or abnormal. clearly some animals do fail the test completely (e.g. budgerigars and beta fish, who respond to reflections with affection/aggression, the way they would when confronted with a separate creature), and clearly some few non-human animals which are capable of self-consciousness, but there's a decent-sized grey area in between. --Ludwigs2 14:29, 12 June 2010 (UTC)

Wouldn't that be easy to check by first placing the paint somewhere that the cat doesn't need a mirror to inspect? I have a difficult time imagining a cat, looking down at its own paw and not being irritated by something that a researcher did to its fur. APL (talk) 15:28, 12 June 2010 (UTC)

you'd have to be careful not to be confused by cats' normal irritation at being messed with. for instance, if you were to put a cat under anesthesia first (so it wasn't aware of the process) and dye its paw blue, I am not at all sure how much the cat would be disturbed by its newly blue paw, assuming the dye was tasteless, odorless, not irritating, etc... Clearly primates would be disturbed by such things (as demonstrated by numerous pranks played on drunk dorm-mates), but cats and dogs? remember, cats and dogs are often taken if for grooming, which can involve extensive changes in bodily appearance as fur is shaved away, but they are not generally perturbed by it. --Ludwigs2 16:35, 12 June 2010 (UTC)

Clearly it implies that the cat does not fully understand mirrors, if it's treating the reflection and the person as separate entities. But I'm not sure that it even implies that very strongly. Even if it does understand mirrors it might be treating it as a separate entity for amusement. Cat's like toys. So I'm not sure that it proves or even strongly implies anything.

Anyway, The point of the mirror test is not to check if the animal understands mirrors in general, but to check if they can recognize their own image. APL (talk) 15:28, 12 June 2010 (UTC)

It surprises me how much importance people place on mirror recognition. For a cat to recognize its reflection in a mirror is not in principle different from recognizing its own paw when it looks at it -- the fact that the light bounces off a reflective surface before reaching the eye has no philosophical significance. All animals that are capable of damaging their own bodies need robust self-recognition mechanisms to prevent that from happening, and mirror recognition is just that same process in action, as far as I can see. It raises a number of interesting practical issues, certainly, but I don't understand why it would raise philosophical issues. Looie496 (talk) 17:21, 12 June 2010 (UTC)

This brings to mind the all the times I've seen cats fail to recognize their own paws, and accidentally start washing the furniture. 213.122.16.179 (talk) 19:23, 12 June 2010 (UTC)

Breathable boots

I was watching How It Works earlier and it showed a factory making breathable, waterproof boots using Gore-Tex. The commentator said that it keeps water out whilst allowing steam/sweat to leave because these molecules "are 20 times smaller than water molecules". I call bullshit on that, water molecules and steam molecules are going to be the same size because steam IS water, with more kinetic energy and less dense. This also raises the question of why steam would need to escape. As far as I'm aware, human feet don't get hot enough to generate steam! So how does this system really work? Regards, --—Cyclonenim | Chat  11:12, 12 June 2010 (UTC)

(commentator's explanation was wrong)

Goretex (which see) allows water vapour out via the tiny holes, but doesn't allow water droplets in. As you know water droplets tend to stick together, and thus do not tend to break up - so they don't/can't break into tiny water droplets to go through the tiny holes.77.86.125.56 (talk) 11:18, 12 June 2010 (UTC)

Also, water vapour forms below 100C - eg evaporation - when you sweat the water evaporates, but your skin is not at boiling point, the difference is that air below 100C can only have a certain smaller amount of water vapour in it.77.86.125.56 (talk) 11:21, 12 June 2010 (UTC)

Boiling point is the point where the pressure of the water vapour (see vapour pressure) is the same as the ambient pressure, which allows bubbles to form and rise to the surface, allowing very rapid evaporation. The amount of water vapour that can remain in the air is related (that amount is the vapour pressure), but it isn't the key difference, since it is a gradual change. --Tango (talk) 02:15, 13 June 2010 (UTC)

I would expect that condensation on the cool inner surface of the boots from the warm vapour from your warm body is going to ruin the breathability anyway. 92.15.30.42 (talk) 11:52, 12 June 2010 (UTC)

Grass in flower beds

I've always had a problem with lots of grass growing in my flower beds. I have two situations: a) ground dug up in the early spring, annual flower seeds sown. b) perennial or biannual plants sown last year, so the ground could not be dug over - the bed looks like uncut grass with leaves in it. Is there any solution to getting rid of the grass except pulling out every grass blade one by one, a Herculean task? Thanks 92.15.30.42 (talk) 11:44, 12 June 2010 (UTC)

Not really enough detail on what the plants are to answer this, and you might be better off in some of the excellent gardening forums around on the web. Depending on the perennial plants but in general grass is not very good at pushing through wood shreddings compared to many (but not all) perennials. Strimming down the grass as much as possible and then spreading a 2in layer of bark or wood chip over everything might work. --BozMo talk 12:46, 12 June 2010 (UTC)

That would probably kill all the plants as well though. 92.15.0.254 (talk) 18:08, 12 June 2010 (UTC)

This depends on whether the grass is perennial creeping or whether it is annually seeded. If it is annually seeded then you need to get on the job at regular intervals in the spring and summer and pull it out before it seeds. If the grass is a creeping perennial type then you have a much harder problem to solve. No amount of pulling out will kill the grass in the long term because you will almost certainly leave bits of root behind which will regrow, and they will come through wood chips without a problem! For perennial grass you will either have to dig up the whole plot at some point that will not disrupt the flower display or by very carefully using a small brush to apply herbicide to the grass - of course I understand this might be totally impractical. First determine by the careful removal of a dozen or so sample grass plants if they are annual (self-contained clumps with fine roots) or perennial (attached to underground spreading roots). It may be a mixture of both types. I hope for your sake it is the former. You are not alone [5] Caesar's Daddy (talk) 14:57, 12 June 2010 (UTC)

For particularly tough grass such as (couch grass), I find that the best solution is glyphosate weedkiller applied with a paint brush so as to avoid affecting the nearby plants. This requires lots of patience, but it is very effective. Dbfirs 15:47, 12 June 2010 (UTC)

Do you think it would work if I applied the weedkiller during the winter? Thanks 92.15.0.254 (talk) 18:12, 12 June 2010 (UTC)

The plant has to actually be growing, and not dormant to be killed in this way with glyphosate, but if your winter is warm enough for continual growth it should still kill it. Graeme Bartlett (talk) 21:56, 12 June 2010 (UTC)

gear box vs belt pulley

For an 18 KW motor (~25hp), I use a 'v' belt (c type) to convert the speed from 900 to 450 rpm. An alternative is to replace this with a gear box. I believe the advantage of the gear is higher efficiency although with maintenance issues. Now without having actual data about the difference in efficiencies of the 2 and the annual/monthly maintenance cost involved with the gear box, is there any reason to prefer one over the other? The load connected to the motor is prone to slight vibrations every now and then. Thanks —Preceding unsigned comment added by 122.169.217.4 (talk) 13:06, 12 June 2010 (UTC)

Wear on the belt system is primarily on the belt - maintenence is replace the belt, compare this with maintenence on the gears (which may not even be possible - once the teeth are worn that's often it.) - the device will be out of action for much longer.

87.102.84.163 (talk) 15:13, 12 June 2010 (UTC)

What about a chain drive?87.102.84.163 (talk) 15:19, 12 June 2010 (UTC)

Actually summarised here [6] one big factor is if slip is acceptable, and the size of those torque variations.87.102.84.163 (talk) 15:22, 12 June 2010 (UTC)

Vellus hair

In Vellus hair it is said that exceptions (for vellus hair) include the lips, the backs of the ears, etc. The back of the ears usually has a very soft down generally and a few thick strands of hair occasionally. Isn't this an error then/?--117.204.94.179 (talk) 13:28, 12 June 2010 (UTC)

Pure OR of course, but the backs of my ears lack any hair apart from a few thick strands on the edge of the helix. Mikenorton (talk) 14:54, 12 June 2010 (UTC)

The backs of my ears are hairless but those of my cat are furry. I changed the title for easier reference. Cuddlyable3 (talk) 16:45, 12 June 2010 (UTC)

Are you sure? Those hairs are usually not dark and very short and almost invisible. You can try to pick them closely between two fingertips. Maybe, they are visible when you stand against bright sunlight as coming through the door way of a bright morning.--117.204.82.21 (talk) 01:41, 13 June 2010 (UTC)

You could have some moles on the backs of the ears that produce dark hair, I suppose. --Tango (talk) 02:10, 13 June 2010 (UTC)

No, not growing on moles. I am talking of a soft, fair down. Unfortunately I don't have a girl friend now to check it with somebody else. --117.204.88.50 (talk) 05:14, 13 June 2010 (UTC)

How to get a sponsorship

Hello,

My research paper has got selected in an international conference by IEEE http://www.icmee.org/ . I was a student of my college a month ago when i submitted that paper.Currently i have passed out.So,i could not find that how could i arrange the huge sponsorship amount.scientists at that end,Kindly help.I have just graduated in b.tech mechanical Engineering. Pardon me for asking an off topic question. Sameerdubey.sbp (talk) —Preceding undated comment added 15:23, 12 June 2010 (UTC).

Welcome to the harsh world of science. You have to find funds to do research, it seems to me the most appropriate way in your case would be to apply for a Ph.D research position... 15:51, 12 June 2010 (UTC)

You could do well to write to people who work in your field of interest. Let them know that you know about their work (from publications?) and tell of your own. Suggest that you would like to meet at the conference. Listen to and value their advice. Cuddlyable3 (talk) 16:29, 12 June 2010 (UTC)

Your question is not entirely clear. Are you asking how you might obtain funding to cover the costs of attending the conference, or funding to cover the costs of continuing your research? If you need funds to attend the conference, I would be surprised if the college you were a member of cannot give you either a small grant for this purpose, or at least advice on where to apply elsewhere for one, since your achievement must reflect well on them. If you need funds to continue your career, again your former college ought to be able to give you advice, but attending the conference, talking to more senior scientists there about your paper, and asking them for advice or directly for employment would be one strategy. 87.81.230.195 (talk) 17:45, 12 June 2010 (UTC)

The OP is probably in India, where money does not grow on trees, and the conference is in Japan, which is expensive to visit. But the reality is that if the supervisor of the project can't fund the travel, it is unlikely that anybody else will. Some academic conferences pay for travel for a certain number of students, but IEEE is more business-oriented and probably doesn't. I should also point out that IEEE conferences generally accept everything that is submitted to them, so having a submission accepted isn't a mark of prestige. Looie496 (talk) 17:53, 12 June 2010 (UTC)

Sameer, I notice that quite a number of people on the Program Committee are from India. If one of them happens to be from your own college, or from nearby, you could contact him to ask for suggestions. Looie496 (talk) 18:06, 12 June 2010 (UTC)

One thing to bear in mind is the OP didn't actually say where their university/college was located. The OP is probably from India, but whether their university/college is there wasn't stated. I initially thought the OP has been studying at the US because they said 'college' but on second thought if they were doing a B.tech in ME they may have done it at something called a college in India. Nil Einne (talk) 22:40, 12 June 2010 (UTC)

Using sea water in toilets

What are the difficulties in using sea water (directly, without desalination etc) in Flush toilets ? Barring the additional cost of plumbing and also the problem of corrosion of the taps etc (which I suppose can be solved by using plastic or other corrosion resistant materials), what prevents us from implementing this ? It would save a lot of water (approx 20 liters per flush) - WikiCheng | Talk 17:01, 12 June 2010 (UTC)

A third problem is that waste water is treated with bacteria before the water is drained to seas/rivers/whatever, and currently known efficient bacteria won't live in salty water. If you manage to bioengineer salt resistant bacteria (if you are into biotech, there's a nice project for you, go for it!), I guess you are pretty much left with the financial equation: desalinate vs. invest in duplicate pipe systems. Or triplicate: where I live we have two drain systems, one for rainwater and one for sewage; salt water sewage might require a third one, unless you want to mix your kitchen sink sweet water sewage with the salty toilet sewage. 88.112.56.9 (talk) 17:20, 12 June 2010 (UTC)

The article Head (watercraft) notes the use of sea water to flush toilets on boats. In submarines the high external water pressure makes this difficult. Cuddlyable3 (talk) 17:49, 12 June 2010 (UTC)

One could also ask why we don't use grey water in toilets. I can't say for certain, but I imagine that it's primarily the difficulty of running/maintaining the extra set of piping and storage, rather than any properties of the water itself. Fresh water is still cheap enough in most places (especially with low flow toilets) not to be worth the hassle. Also, getting the sea water to Nebraska (or even 100 km inland) would be a hassle. -- 174.24.195.56 (talk) 18:02, 12 June 2010 (UTC)

Using industrial quality water is toilets is pretty common wherever it's cheap enough to have two sets of pipes (or simply not to pipe drinking water). Physchim62 (talk) 20:21, 12 June 2010 (UTC)

They have been doing exactly that in Hong Kong for quite a while now (see Water supply in Hong Kong). But unless it's a densely populated coastal city the cost of laying and maintaining 2 sets of pipes might more than offset the cost and fresh water savings. --antilived^{T | C | G} 01:39, 13 June 2010 (UTC)

Unless you also have separate sewers, using seawater would actually be harmful. If your home is connected to a sewer system, you can't really "waste" water. Any water you use is recycled by the next city downriver from you. (Each city picks up water from the river, uses it, treats, and puts in back in the river for the next city downstream to use.) So it should be obvious that putting salty water in a freshwater river is something you should avoid, both for the river itself, and also for the next city downstream. Home Kong probably has no one downstream - they probably dump their sewage into the ocean. Ariel. (talk) 09:56, 13 June 2010 (UTC)

They use sea water on oil platforms to flush the toilets. There is at least recorded accident because the same sea water system was used for heat exchangers for cooling live crude as well. The sea water had jammed up every directional valve and corroded through the heat exchanger resulting in a flammable gas mixture being evolved into the toilet through the cisterne. Someone was smoking on the toilet (am pretty sure the whole platform was a non smoking zone although the toilet was in the crew "safe haven") and got a nasty surprise. Which highlights I guess that handling seawater through conventional plumbing is not straightforward. --BozMo talk 13:55, 13 June 2010 (UTC)

Thanks for your answers ! I forgot to mention the phrase 'at least in the cities near the sea' in my question :-). But I am surprised that it seems to be an issue of cost and preventing accidents (as stated by BozMo) rather than any technical problem - WikiCheng | Talk 04:04, 14 June 2010 (UTC)

Watering plants

Is it beneficial to urinate over garden plants? Or would the salt in the urine be harmful to them? A Wikipedia article says that drinking urine in survival conditions should never be done due to its salt content, so would urine be harmful to plants too? 92.15.0.254 (talk) 18:20, 12 June 2010 (UTC)

They'd get burnt from the acid too. YOu should see what female dog urine does to lawns! --TammyMoet (talk) 19:38, 12 June 2010 (UTC)

Yes, mostly the acid. Try urinating over a test plant, if you wish. You will quite quickly (one or two weeks of regular urinating, I'd say) that the plant turns brown and dry, just as if it were dead from lack of water. However, I know from observation of urinated-over lawns that some plants, especially some species of moss, survive the urine and thrive, whereas grass is burned. Of course the moss then makes it harder for the grass to grow back. In short, unless you want a moss garden, don't. --Alþykkr (talk) 22:33, 12 June 2010 (UTC)

I would guess that the moss is still being harmed by the urine, just not as much as the grass, so benefits from the lack of grass. The benefit from there being less grass around could very easily be greater than the harm from the urine. --Tango (talk) 02:09, 13 June 2010 (UTC)

(Edit Conflict) Actually wetting plants with urine would, as already stated, probably 'burn' them, but (human) urine is a useful source of nitrogenous fertilizer for the soil; discussions of this I have heard/read in the past usually recommend storing it for a time in a (sealed) container rather than adding it 'fresh' (just keep a plastic screw-top bottle next to the toilet, and add to it as and when). Googling on "Urine gardening" returns many hits discussing the topic in detail. 87.81.230.195 (talk) 22:37, 12 June 2010 (UTC)

This is a common question on "Gardener's World" type programs. The consensus seems to be you should wee on your compost heap but not directly on to plants. All the panelists last time I heard this on the radio admitted they did this (even the ladies) although there were technique variations. --BozMo talk 14:05, 13 June 2010 (UTC)

On the other hand if they are weeds and your urine does kill them would seem an effective and fairly safe weed killer Nil Einne (talk) 06:03, 14 June 2010 (UTC)

And I should add that the salt in urine is very dependent on Diet, at least for NaCl. My Dad was some type of Diabetes specialist [7] who served as a ship's doctor on a Destroyer in the med in WW2 where sailors refused to take their salt tablets. He was fond of saying that when people were running salt deficit their urine had a lower salt content (meaning NaCl) than laboratory distilled water. He had measured it of course. --BozMo talk 10:37, 14 June 2010 (UTC)

brushed nickel

what is brushed nickel ? and can it cause dermatitis —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 20:05, 12 June 2010 (UTC)

See Nickel#Toxicity. hydnjo (talk) 20:25, 12 June 2010 (UTC)

yes but is brushed nickel the same as reg. nickel does it have a coating —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 20:29, 12 June 2010 (UTC)

According to the WP article "Brushed metal" it is perhaps hot rolled, annealed, pickled and passivated. Of course it can be coated (as anything else) but I don't think that's what you were asking. hydnjo (talk) 20:57, 12 June 2010 (UTC)

Rechargeable Battery: voltage rebound

When a device powered by rechargeable batteries depletes the battery, it stops working because the voltage is not high enough to power it. But I've noticed that if you leave the power off for a while, the voltage of the battery rises without charging. And if you wait long enough (10 min - 1 h) and then turn the device on, the it will work again, although probably with a low battery warning. I have seen this happen in cell phones, cameras, gameboys, and any device using rechargeable AA/AAA batteries.

What causes this voltage rebound? I'm taking about the NiMH and Li ion types mainly. --Yanwen (talk) 21:29, 12 June 2010 (UTC)

This is common across all cell types and is caused by Polarisation: "An effect produced upon the plates of a voltaic battery, or the electrodes in an electrolytic cell, by the deposition upon them of the gases liberated by the action of the current. It is chiefly due to the hydrogen, and results in an increase of the resistance, and the setting up of an opposing electro-motive force, both of which tend materially to weaken the current of the battery, or that passing through the cell." The effect vanishes when the battery is allowed to rest with no current. I'm looking for a Wikipedia article on this. Do we have one? Dbfirs 21:38, 12 June 2010 (UTC)

Depolarizer ? Battery chemistry is quite a big topic - I'm suprised there isn't more here.

Thanks, 87, I'd missed that. The effect still seems to be called polaris(z)ation, even though the chemistry varies. Dbfirs 07:57, 13 June 2010 (UTC)

... also from the history of cells at "Battery and Energy Technologies" [8] "Volta's simple voltaic cell cannot operate very long because bubbles of hydrogen gas collect at the copper electrode acting as an insulator, reducing or stopping further electron flow. This blockage is called polarisation. Daniell's cell overcomes this problem by using electrolytes which are compatible with the electrodes. Thus the zinc electrode is suspended in an electrolytic solution of zinc sulphate which is contained in the porous pot (Initial designs used sulphuric acid rather than zinc sulphate). The porous pot is in turn immersed in the copper sulphate solution which is contained in a glass jar into which the copper electrode is also suspended. The Daniell cell does not produce gaseous products as a result of galvanic action and copper rather than hydrogen is deposited on the cathode. Daniell's non-polarising battery was thus able to deliver sustained, constant currents, a major improvement on the Voltaic pile." The chemistry will be different in NiMH and Li ion types, but the principle is the same. The effect becomes more noticeable as the battery becomes weaker. Wikipedia does have a short paragraph at Primary_cell#Polarization. You might also be interested in this patent application. Dbfirs 21:52, 12 June 2010 (UTC)

The situation in Lithium batteries is different due to lack of production of Hydrogen - a similar effect may be produced in Li cells by locally (near the electrode) increased concentrations of Li+ ions reducing the cell EMF - these will take time to diffuse away. Note:this is one possibility - I haven't got a full analysis of the processes in Li cells.

I think this accumulation of reacted lithium is still a form of (ie is called) polarisation. 87.102.84.163 (talk) 01:03, 13 June 2010 (UTC)

Yes, the 2009 patent (above) uses the term "polarization" for the effect in Lithium cells. The original problem was with hydrogen, but the term just means accumulation of ions or molecules near to one (or both) of the poles. Dbfirs 08:06, 13 June 2010 (UTC)

Cauterization as an emergency measure

Why is it that cauterization is never mentioned as a possible (although obviously... not optimal) way to stop heavy bleeding in an emergency ? Is it only because of practical purposes (the emergency rescuer is unlikely to have a source of heat with him or near him), or because of inefficiency/dangers ? I know cauterization is extremely painful and causes tissue damage, but in the event bleeding can't be stopped even with a tourniquet (or if the tourniquet can no longer be maintained because of risk of limb loss), would cauterization be an interesting last-resort solution ? Thanks in advance, --Alþykkr (talk) 22:28, 12 June 2010 (UTC)

Probably because it is very rarely useful. Even tourniquets often aren't taught on first aid courses these days. Direct pressure, elevation and pressure points can do the job in pretty much all circumstances where tourniquets or cauterization would help. If cauterizing wounds was useful, it wouldn't be hard to include a suitable tool (either gas powered or electric) in the bags paramedics carry, or even in first aid kits. --Tango (talk) 22:58, 12 June 2010 (UTC)

According to the 'SAS survival manual' (probably not really - but that's what it was called, though I believe it was written by an ex-SAS guy) I had as a teen, cauterization is only to be used as a last resort in a situation where no rescue is imminent, say if your plane just crashed in the Andes (or something) and someone's legs are hanging off. There was a caveat that cauterization will actually cause some people to drop dead from shock. --Kurt Shaped Box (talk) 23:07, 12 June 2010 (UTC)

An observation by a nonmedical person: Cauterizing , say an artery after some traumatic amputation smacks of 18th century naval battles. But electrocautery does seem to be used today to stop small bleeders in operations. Edison (talk) 01:31, 13 June 2010 (UTC)

Indeed, it is used for small blood vessels that you can get to precisely. They only touch the cauterizing thing to the blood vessel itself. It is very different to cauterizing a wound from the outside with a big red-hot poker. That means there is no real tissue damage, other than to the blood vessel that has been damaged by severing it anyway. --Tango (talk) 02:06, 13 June 2010 (UTC)