Wikipedia:Reference desk/Archives/Science/2008 December 12

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December 12

cactus

are all or most Echinopsis cacti phycedelic? —Preceding unsigned comment added by 76.14.124.175 (talk) 01:57, 12 December 2008 (UTC)

Hi – it looks as though almost all are psychedelic. At Echinopsis pachanoi, Echinopsis macrogona, Echinopsis scopulicola and Echinopsis lageniformis it mentions psychedelic effects. On a quick reading, they could be mistaken for other closely related cacti that may not have the same properties. There's a list of species at Echinopsis if you'd like to check through the blue links in the species section. Julia Rossi (talk) 02:36, 12 December 2008 (UTC)

Detecting bullets and Improvised Explosive Devices

Could a 360 degree angle, super fast, super high definition video camera with a computer vision system continuously comparing images help soldiers if Afghanistan by (1) detecting tiny changes in landscape features such as soil disturbance in the case of IED's and (2) detect the direction bullets come from so the soldiers know where to return fire and avoid getting shot or killing the wrong people? I make the assumption that for IED detection multiple drone or airships regularly update the data. Could some sort of radar or lidar be used to detect the source of flying bullets? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 04:08, 12 December 2008 (UTC) Trevor Loughlin (talk) 04:09, 12 December 2008 (UTC)

Bullet detection systems (which basically tell you where the bullet came from) are already in use in the military: [1].

A 360 degree camera would need astounding resolution AND an incredible frame rate to be able to detect things as small and fast as bullets. Hence, the Qinetiq system uses sound.

UAV's look down on the scene from high altitude with cameras that have a narrow field of view and very high precision. Whether the people who analyse these photos can use them to detect an IED seems rather unlikely though - they are often placed under existing roadside features like trash piles and so forth.

SteveBaker (talk) 05:24, 12 December 2008 (UTC)

I've always wondered why they don't go all the way with the sniper detection systems and wire them into a weapon on top of a Humvee. If anyone shoots a bullet towards you, their location gets an RPG in return. --Sean 14:50, 12 December 2008 (UTC)

Because putting fire control in the hands of an automated system is a very touchy proposition. Consider that a system like Qinetiq cannot distinguish who fired a round or where they aimed, or often even how far away they are -- only a bearing to point of origination is provided. — Lomn 15:24, 12 December 2008 (UTC)

Fire control tightly couples into the rules of engagement. In many combat situations, even humans are not allowed to fire on a target without explicit case-by-case permission from a superior officer. As for the "super-high-resolution visual detection" problem, there's a variety of issues - the quantity of data processed becomes immense. Covering a large amount of ground with cameras increases the amount of data to process. Detecting "events" becomes a very hard computer vision problem; distinguishing "threat" events from "non-threat" events becomes a very hard artificial intelligence problem; and then, what to do as a response? If every square inch of a city is covered with a surveillance system, that does not necessarily mean there are adequate resources to respond to all detected threats. These topics are definitely under research; I've seen presentations on various technologies which aim to assist in this direction. It's pure speculation whether these systems will ever become functional and cost-effective enough to see common usage. However, if you think of the technological augmentations like RADAR and night-vision, which fifty or eighty years ago were "crazy ideas", they are now common-place in a lot of militaries... Nimur (talk) 15:35, 12 December 2008 (UTC)

I think that the reasoning is even more simple than that. It's the 'what if it malfunctions and starts firing indiscriminately at everything that moves?' factor that makes people jittery about deploying what basically amount to automatic sentry guns. --Kurt Shaped Box (talk) 16:33, 12 December 2008 (UTC)

This system actively identifies objects as small as RPGs using radar. I think it's on the edge of what radar can do right now. My friend is just preparing to head off to his second tour in Afghanistan. He said that one of the major problems with finding underground IEDs was that most areas of Kandahar relied on artificial irrigation agriculture. There were always holes and piles of dirt and people walking around with shovels. I'll bet a probability-based-system could be designed to give soldiers good estimates of where soil-buried IEDs could be. But IEDs tend to find themselves under piles of rubbish, in broken down automobiles or other already "irregular" features in the terrain. NByz (talk) 08:17, 13 December 2008 (UTC)

A UAV looking down and using thermal imagery would often show the location from which shots were fired. I have seen cop helicopter videos wherein a gun tossed from a moving car shows up glowing brightly in IR imagery lying in the weeds, and the heat given off by a human makes him show up clearly as well. The gun and the bullets would show up nicely via infrared. If the command and control forces knew where friendly forces were, it would be simple for the UAV to fire missiles at the source of the enemy firing. The downside is that mistakes are frequent, such as a US pilot bombing Canadian soldiers in Iraq, or US helicopters firing missiles at US light armored vehicles in Iraq. This also only works in conflicts where high-tech forces are up against poorly equipped forces, since a state-of-the-art military would promptly shoot down an enemy UAV, or if friendly forces had beacons of any sort to identify themselves to friendly aircraft, a state-of-the-art enemy would target missiles on those beacons. Edison (talk) 16:14, 12 December 2008 (UTC)

I know it's minor, but being Canadian, I wanted to mention that Canada wasn't involved at all in the invasion of Iraq. I think that you're thinking of the Tarnak farm incident in Afghanistan. Interestingly, according to our article on Iraq War (search "canada") Canada had one blue-helmet observer in Iraq in 2006... fancy that. NByz (talk) 08:21, 13 December 2008 (UTC)

It's really not much different than wearing a uniform: it doesn't have to transmit anything, it just has to be identifiable to a friendly unit. SDY (talk) 17:27, 12 December 2008 (UTC)

Soldiers wear camo when in combat, not (in modern times) gaudy uniforms. U.S. and allied forces sometimes had strobes on their persons and vehicles so that airborn gunships could tell them from hostiles forces in Iraq. If the enemy had modern technology, and aircraft the strobes or many RF identification methods would have been a death sentence. Edison (talk) 19:11, 12 December 2008 (UTC)

It's a tricky problem - you need your own troops to send some form of signal to the aircraft (or to each other) to say "don't shoot me" - but that carries with it two problems:

1. The enemy may learn to duplicate that signal and then you won't be able to shoot at them.
2. The enemy may be able to pick up your signal and use it to find you when you're trying to hide.

So - bright uniforms and strobe lights definitely fall foul of both of those problems. Something like a GPS reciever with a transmitter that sends out your position in an encrypted data stream would solve (1) because effective encryption would make it impossible for the bad guy to create a message that says "don't shoot me" for his coordinate - simply repeating the good guy's message would just reinforce the good guy's protection from friendly fire. But any kind of radio transmission will reveal your location if the enemy is sufficiently smart - so this falls into problem number (2). You could go with a 'challenge/response' system where the attacking aircraft sends a message to the target and if it fails to respond with an encrypted GPS position that matches the target coordinate...then you shoot. That means that the aircraft doesn't give away its position until a couple of seconds before it's about to fire and and reveal itself anyway...and forces on the ground don't broadcast their position unless they are about to suffer friendly fire - and in all likelyhood they'd be better off not being fired on, so it's worth the risk of being detected. So this could be done with almost complete safety.

SteveBaker (talk) 04:05, 14 December 2008 (UTC)

Since most people seem to concentrate on the second question, here's some info on the first. The Rafael RecceLite pod recently got an upgrade to perform exactly what you propose, the fully automated finding of landscape changes to detect possible IED sites. - Dammit (talk) 14:28, 14 December 2008 (UTC)

Water waste

I don't really understand why using lots of water is considered an environmental issue. The earth is a closed circuit, and as I understand it, most of the water from showers gets run off into the water system, purified, and reused, right? So how is it an environmental issue to take longer showers or water one's lawn (when it isn't an immediate drought)? 140.247.152.90 (talk) 05:07, 12 December 2008 (UTC)

Its not, apart from usually electricity (and hence coal) is used to pump the water. Many places actually have limited amount of water that because their damns only hold so much. When there is alot of water people use rediculous amounts for pratically anything. I believe it something like 5000 tonnes of water to make a laptop for example.--155.144.40.31 (talk) 05:30, 12 December 2008 (UTC)

(EC with above) The issue is not in the global use of water, it's in localized use of water. While on the whole, water is recycled via the water cycle, at the local level there are limited clean water resources in any one place. Wasting water lowers the amount of availible water, in say your local resevoir or underground aquifer and thus is of concern to the other people who share that water supply with you. In many places prone to drought conditions on a semi-periodic basis (such as the American South since about 2000) municipal water supplies dwindle to dangerously low levels on an annual basis. In other places, such as the American Midwest, the drainage of major underground water suplies, such as the Ogallala Aquifer is a serious concern, since such aquifers are slow to replenish; the annual removal of water from such aquifers frequently exceeds natural processes ability to replace them. The earth as a whole is not running out of total water, but the amount of potable (i.e. usable) water supplies is quite small, and subject to major problems if not managed well. --Jayron32.talk.contribs 05:33, 12 December 2008 (UTC)

Thanks. So, followup. This question arose cause the dining hall I eat at at college is considering going "trayless" (no trays to put your plates on) as a way to save, among other things, about a half gallon of water used to clean each tray. But we're in upper east coast America in a major city. Is running out of potable water a serious issue? Or is that a "waste" that's really meaningless? Thanks again, 140.247.152.90 (talk) 05:50, 12 December 2008 (UTC)

Not sure what "upper east coast" you are, bu the Mid-Atlantic states head towards drought nearly every year that I can remember, with lawn-watering and car-washing restrictions to conserve reservoirs. Some years I remember use restrictions in Manhattan (not lawn-watering, obviously:) and even up into Connecticut. Even little things that seem innocuous apparently make a big difference...first sign of drought, restaurants start serving water only when requested rather than by default when you are seated. DMacks (talk) 06:05, 12 December 2008 (UTC)

(EC with Dmacks response)Well, the other issue I neglected to mention is that waste water itself (the stuff that goes down the pipe at the bottom of the sink) all must be treated before being released back into the environment to remove all the nasties (like poop and soap) from it. This waste, even after being removed, must be dealt with as well. Reducing water usage also has the added benefit of reducing the amount of waste-water that need to be treated. Cleaning trays requires soap, which must be removed from the waste-water, and thus produces additional enviornmental stressors.

Additionally, there is the concern over short-sightedness. Even if, right now, the specific location you live in is not currently under water shortages, there is no reason to suspect that it will continue to lack those problems; no one ten years ago forsaw the current drought in Georgia and the Carolinas. Additionally people in America are highly mobile, and it seems reasonable to encourage good habits across the board, given that you may find yourself living in Atlanta or Phoenix or Kansas City some day; all of which are places facing serious water problems. --Jayron32.talk.contribs 06:07, 12 December 2008 (UTC)

Some people have made some good points although no one has linked to virtual water yet (which will a little simplistic at least helps you think about the issues). And one key point which Jayron hinted at but I will emphasise in a different way is that just because the water is still present on the earth doesn't mean it's easy for us to use. For example if the water all ends up in rivers that are extremely polluted that's a problem. And perhaps a far bigger issue is that while we can desalinate water, it remain an incredibly expensive process. Therefore if a significant proportion of our fresh water ends up in the sea we start to have problems. While yes, this water should eventually make it back to land (somewhere) as fresh water this may not happen as fast as we used it depending on the source. Not surprisingly then may have suggested the number of wars fought over water is going to increase in the 21st century. The water article has numerous links that may be of some interest, e.g. water politics and the water cycle also has this "the water cycle to continue to intensify throughout the 21st century, though this does not mean that precipitation will increase in all regions. In subtropical land areas — places that are already relatively dry — precipitation is projected to decrease during the 21st century, increasing the probability of drought. The drying is projected to be strongest near the poleward margins of the subtropics (for example, the Mediterranean Basin, South Africa, southern Australia, and the Southwestern United States)." Nil Einne (talk) 10:23, 12 December 2008 (UTC)

Half a gallon of water to clean one tray? They don't need to stop giving you trays, they need to use more efficient cleaning methods. All you need is a damp cloth... --Tango (talk) 10:30, 12 December 2008 (UTC)

Aramark's promotional literature for trayless dining (oh well, soon I guess) for the higher-ed market states "on average, a tray conservatively requires one-third to one-half gallon of water to wash." DMacks (talk) 11:15, 12 December 2008 (UTC)

I'm was with Tango, but out of interest had a bit of a look into it...If we say the average commercial dishwasher uses 6 gallons per cycle (http://www.hrwet.org/b&i_guide/cafe.htm) that'd mean putting through 12 trays per cycle, which is probably reasonable for a commercial dishwasher to handle (from my restauranter kitchen porter days!). As per the above it is the energy (and chemicals) required to re-clean water that's the best reason to minimize waste where feasible, this seems like a plausible way to reduce waste water. 194.221.133.226 (talk) 11:47, 12 December 2008 (UTC)

A commercial dishwasher is overkill for cleaning trays. There won't be food stuck on them and people won't be eating off them. A quick wipe with a damp cloth, maybe with some antibacterial soap on it (and then another wipe with a plain damp cloth) should be plenty. --Tango (talk) 12:38, 12 December 2008 (UTC)

I would assume that a school will not wash these things by hand. What you suggest would no doubt be enough but I suspect that they are put through the machine like other dishes. Essentially if we say there are 500 students using 1 tray per lunch time you've got a hell of a lot of trays to deal with. If you use a machine you can stack that, put it on (industrial ones i've used take a minute or two) and be doing something else while that does it, then switching to the next. I think they'll put them through the machine more often than not. 194.221.133.226 (talk) 14:13, 12 December 2008 (UTC)

Wiping a tray only takes marginally longer than putting it in a dishwasher - they need to decide which is worth more, an extra second of somebody's time or half a gallon of water. --Tango (talk) 14:17, 12 December 2008 (UTC)

Food service industries are regulated heavily by most states WRT dish cleaning procedures, for sanitation purposes. Most require that all dishes and utensils handled by customers and reused are washed according to certain standards (trays are not exempt); for example that they are washed at a certain temperature water, and according to certain procedures. While dishwashers are one option, and handwashing is another, but it is usually a far more extensive procedure than "wipe with a rag". The regulations exist for sanitation purposes; honestly, I am not sure that I want to eat off of a tray if I knew that hundreds of people ate off that tray before me, and the best it got was a half-assed three second wipe with a damp rag! If the trays are washed properly by hand, it may use somewhat less water, but it would also require significantly more work; more work costs more money; and the added cost of paying several extra people who essentially work to keep trays clean just for you will be added into the cost of the food. Given that option, it is just easier to forgo the tray... --Jayron32.talk.contribs 14:42, 12 December 2008 (UTC)

You don't eat off a tray, you eat off a plate. Paper serviettes could be issued for food items that don't come on a plate (fresh fruit, say), and for cutlery. There is no need for food you are going to eat to ever touch the tray. --Tango (talk) 14:46, 12 December 2008 (UTC)

Exactly... So the tray is superfluous. Good to see you understand that! --Jayron32.talk.contribs 15:12, 12 December 2008 (UTC)

Yes, Jayron, whatever you say, Jayron. --Tango (talk) 16:14, 12 December 2008 (UTC)

They are superfluous for people not purchasing a beverage or side dish. APL (talk) 05:35, 13 December 2008 (UTC)

You also don't eat off a toilet seat (I hope!), but it's a good way for germs to get around because they get on hands and hands get on food which gets... you gets the point. Part of the reason for the "always wash your hands after using the toilet" advice. Institutional settings are notorious for disease outbreaks because of shared stuff, and it's much easier to clean trays than it is to clean tables (which would otherwise have many of the same problems). Cleaning trays is certainly a secondary concern, but it's not irrelevant, especially in high-risk settings like hospitals. SDY (talk) 15:44, 12 December 2008 (UTC)

Which is more "environmentally friendly" - disposable cutlery or reuseable cutlery that must be washed? This depends on so many factors, such as rate of consumption, quantity used; etc. It's not immediately obvious which has less total environmental impact. Nimur (talk) 15:42, 12 December 2008 (UTC)

How many hands does the typical student have? Because carrying a main course, pudding, piece of fruit, drink, cutlery, and then paying at the till may prove somewhat difficult if they typically have two hands each. DuncanHill (talk) 15:47, 12 December 2008 (UTC)

The first reply to this query says something about wasting 5000 tonnes of water to make a laptop...? Wha..? ~ R.T.G 16:01, 12 December 2008 (UTC)

Who does anything more than wipe their toilet seat clean? --Tango (talk) 16:14, 12 December 2008 (UTC)

Suppose the previous Diner A has an infectious disease ("the bug") whose germs or virus can survive for an hour on an environmental surface like a tray. He eats, and transfers the bug from his saliva to his spoon and fork, which he leaves on the tray, contaminating it. The cafeteria worker wipes the tray with a rag which picks up the bug, and which leaves some on the tray. As the worker wipes other trays, he leaves the bug on them. Diner B places his silverware on the tray, contaminating them with the bug, which he then transfers to his mouth, as do diners C, D, .... from their trays which the cafeteria workers rag has spread the bug to. Some of the subsequent diners get sick. Thanks, but I will be dining in a place where the trays (if any) are sanitized per health department regulations. Our local health department forbids any wiping of dishes for this reason. They must air dry even after coming out of the dishwasher. Edison (talk) 16:06, 12 December 2008 (UTC)

Antibacterial soap in the water the cloth is dipped in between each tray would do a pretty decent job of killing such bugs. Wrapping the cutlery in a (recycled) paper serviette, as I suggested, also helps mitigate that problem. --Tango (talk) 16:14, 12 December 2008 (UTC)

(ec) While I think Tango's heart is in the right place, it's asking for trouble to trust that a once-over with a damp cloth (soapy or not) will be sufficient. (Are we also prepared to trust that a minimum-wage cafeteria slave – one who's too low on the totem pole to operate the deep fryer or ladle out mystery-meat stew – is going to do a thorough and comprehensive wipedown of each and every one of hundreds of trays every day?) While (most) people won't eat food directly off the tray surface, you don't need direct transfer from tray to food to harm a consumer. Trays are regularly handled by diners who fail to wash their hands after eating, sneezing, picking their noses, etc. If I touch that tray and then my hamburger or sandwich, I'm screwed. The health-conscious guy who buys an apple and lets it roll around on the contaminated tray is in for a world of hurt. A number of unpleasant infectious diseases can be transmitted this way, including – but by no means limited to – influenza, hepatitis A, and norovirus infection. (Worth noting is that all of those are viral rather than bacterial infections, and that even against bacteria the use of so-called 'antibacterial' soaps is not a magic wand.) A warm, damp, frequently-reused tray strikes me as one of the more effective vectors to spread these illnesses from person to person. (The tray-washer's wet rag is probably a good vehicle, too.) Finding a cleaning strategy that uses less than a half-gallon of water but doesn't incur excessive costs (disinfectant cost, cost of employee time, physical hazard to employees, risk of allergic or other toxic reaction for consumer, risk of transmission of infectious diseases) is a nontrivial challenge. TenOfAllTrades(talk) 16:41, 12 December 2008 (UTC)

Um, how much water is used up by a salmon growing up in the sea? 93.132.146.73 (talk) 16:23, 12 December 2008 (UTC)

Before deciding to get rid of trays, we first need to list the purposes of trays. I can think of two:

1) To allow you to carry many items at once. How can you carry a plate of food, bowl of soup, drink, utensils, napkin, and maybe a desert with just two hands ?

2) To catch spills. My soup regularly jostles a bit as I carry it, and spilling those drops on the tray seems far better than on me, the floor, and the table. This could possibly be addressed by putting lids on all the containers, but there goes the dish-washing savings. You could also put disposable lids on the containers, but that's not good for the environment, either. StuRat (talk) 16:51, 12 December 2008 (UTC)

You could, ya know, go up more than once, so that you don't have to take all the food back at once. Many university cafeterias are "buffet" style, where you pay an entry fee, and then its all-you-can-eat. In these situations, another problem with trays is that it encourages people to overload, which then results in food wastage. With a tray, you load up as much food as you think you may eat, and then if you don't finish it, it all goes in the trash... If you have to go up and get your soup, sit down, eat it, go up and get your salad, sit down, eat it, get up and get your chicken, sit down, eat it; you are MUCH less likely to take more than you want... Again, another side benefit of forgoing the tray. Again, NO system is foolproof, and trays come with as many problems as the benefits they provide. The question is if we are ready to forgo the benefits to also avoid the problems. Such is life. There is no perfect sitution ever which allows you to have a perfect system where the choice is obvious. Hence, TAANSTAFL... --Jayron32.talk.contribs 17:29, 12 December 2008 (UTC)

Based on a recent news story about a local university cafeteria which had gone trayless, it seemed to me that the "people take/waste less food if they don't have a tray" was the real reason administration had for the switch, with "it uses less water, so it's better for the environment" being marketing to help convince students to go along with it. -- 128.104.112.113 (talk) 19:45, 12 December 2008 (UTC)

To be fair, having people take (and waste) less food is also better for the environment. This page notes that it takes about 150 gallons of water to produce one pound of wheat. Depending on the location, some substantial fraction of that may come from natural rainfall.) Saving a half gallon of water by not washing a single tray allows one to grow an extra 1.5 grams (about a twentieth of an ounce) of wheat. Trimming the use of meat has an even bigger environmental savings. Reducing portion sizes slightly has a tremendous environmental benefit far beyond the water and energy savings associated with abandoning trays. TenOfAllTrades(talk) 23:14, 12 December 2008 (UTC)

"Trimming the use of meat has an even bigger environmental savings." Depending on what the meat is and where it was raised... 79.66.58.154 (talk) 23:47, 12 December 2008 (UTC)

Although most of the Earth is water, only about 1% of that water is accesible fresh water, and even less is used for safe drinking water. If our water goes into the sewage, it may eventually make it back into our drinking water, but that will take a while to purify. When it rains, water often runs into storm drains and do not get purified, and run directly into the lake. Also, we may not run out too soon, but with looming issues such as global warming and environmental change, drought and other factors could reduce our available water supply even further. Consider that half a billion people rely solely on the water supply from the Himalayan glaciers...and those glaciers could all melt before the century is out. Most of the consequences from not conserving are usually indirect and unintended. While it's true that the Earth is a closed system, that doesn't mean we'll always have the same amount of accesible, clean, safe drinking water. ~AH1^(TCU) 00:07, 13 December 2008 (UTC)

I'm somewhat doubtful of that. While the effiency of raising meat varies greatly, it's always going to be an incredibly expensive process compared to agriculture. You can probably get some decent stats from global warming related studies which although focusing on CO2 likely have relevance to water too. For the person who asked about 5k tonnes for a laptop, again I suggest you take a look at virtual water which while as I said a little simplistic concept (as the article states) begins to address the issue. I suspect 5000 tonnes is wrong. Perhaps 5000 litres. According to our article a car takes between 400k to 1 million litres so 5k tonnes or 5 million litres for a laptop definitely seems excessive. (Although these things are difficult to quantify, definitely agricultural based goods use a lot e.g. 3k4 litres for 1 kg of rice) Nil Einne (talk) 00:38, 13 December 2008 (UTC)

Quote from Virtual water "One needs to understand how internal water resources are being used to produce cars, bicycles, teacups, and the like - particularly because industry usually uses only blue water for production (though rainwater harvesting is becoming more common). On average, a 1.1 tonne passenger car has about 400,000 liters of water embedded in it. This fact is compiled from several different resources including the UNESCO-IHE study[5] and the Australian Food & Grocery 2003.[6] Another source suggests Australian cars require one million litres of water, though this is from using a different method.[7] The construction of house, using a combination of methods, requires about 6 million litres of water.[8]" It is dubious to say the least, referencing four sources of which one is a broken link, two are innaccessable and the last one reveals a pdf document with claims that producing floor space in a certain building type requires 20,000 litres of water per square metre. At best this concept is difficult to grasp and unlikely to be a good guide to water consumption when producing building materials. I have trained up on manufacture of metal parts which requires water cooling and the water is continuously recycled on each machine meaning that only a few litres per day are used although a several dozen litres worth may flow over the tools each day, water never flows out only gets poured in to the resevoir mixed with coolant oil. As I say, I have an inkling about making engine parts and using thousands of litres of water in something as small and simple (simple by comparison) as a car engine accounting for the way the machine recycles the water (coolant) seems to me a difficult number to achieve even if wasting the water on purpose. All water wasted would be stuck to the waste metal not pumped out. It may be different on assembly lines because the manufacture is usually done with high tech robotics which I have never used but I can't imagine some guys rebuilding a classic car engine with lathes and milling machines (which is what the robots use as well) were wasting a couple hundred thousand litres of water without frequent visits to the toilet. ~ R.T.G 03:44, 14 December 2008 (UTC)

"On average, a 1.1 tonne passenger car has about 400,000 liters of water embedded in it. " - this statement is ridiculous. If that amount of water were "embedded" in the vehicle, it would weigh 400,000 kilograms (~ 800 tons). There is an immense difference between water "used for production" and "water embedded inside it" - in that the water used for production has now gone somewhere else - hopefully, through some method, eventually back into the clean water supply. The waste-rate of the supply-line is more relevant than the net quantity of water used. Nimur (talk) 16:04, 14 December 2008 (UTC)

errr - 400,000 kilogrammes = 400 tonnes, or just short of 400 tons. DuncanHill (talk) 16:16, 14 December 2008 (UTC)

While I agree the concept is a little simplistic, I think you're missing the point which is that the water is used and needs to make it back into the clean water supply somehow. That's why it's called 'virtual water' the water isn't literally embedded in the product. I would agree embedded isn't the best word, embodied or virtual is better but nitpicking over the word here doesn't help much. I don't think there is anyone who is stupid enough to think that a car literally contains 400 tonnes of water or that 1 kg of rice contains 3.2 tonnes (IIRC) or water. The main point is, if your country (or whatever) has a very limited level of potable water you're effectively using all that water for this purpose which is therefore unavailable for other uses within your country until and unless it's recycled (which as many people have pointed out is often not as easy as it seems). As I've said several times, the concept has flaws as highlighted in the article, but IMHO the points you've raised are not really it. Nil Einne (talk) 16:13, 14 December 2008 (UTC)

Sorry for my silly arithmetic error... but nonetheless, I still think "virtual water" is a useless concept, because it has no information embedded in it about how much post-processing is needed on the water. As 93.132.146.73 pointed out, you could start talking about a salmon requiring tens of millions of liters of "virtual water" - but if the impact on each liter is negligible, it's far less disruptive than, say, dumping a single liter of bleach into a lake. My contention is that "quantity of water involved" is a silly metric to use for comparing different processes. There is so much variance in the method of water use, that this virtual water concept provides no insight or actionable information. Nimur (talk) 16:55, 14 December 2008 (UTC)

While I can't speak to your experience making engines, I should note that if you're rebuilding a classic car you already have a lot of parts there and you buy a lot of stuff premade which you seem to be forgetting to take into account. Note that if you want to calculate things properly, you need to start from the ground up. Extracting the iron from ground (or wherever it comes from), making steel with the iron etc. That would include all costs from workers (for the time that they work and transport costs) to energy (most power production methods cost some water). You also have to account for the cost of making leather, paint and all the other components. I highly doubt most people rebuilding customer cars raise cows for the leather for example. Or make extract their own iron and make their own steal. Nil Einne (talk) 16:13, 14 December 2008 (UTC)

I don't like most of the answers so far. Water is only in limited supply if you can't purify impure water to an acceptable degree. There is PLENTY of water out there - and it's pretty much a renewable resource (we don't turn much water into other things - and quite a few processes (such as burning oil) actually produce new water. The problem is that the water is mixed up with a bunch of other stuff that we don't want - salt or sewage or chemical pollutants. Assuming that natural purification systems can't keep up (and they clearly can't), we'll just have to do it ourselves. Hence, there are two problems with having enough water...one is to have the capital investment to build purification systems - the other is to have the energy to keep them running. The latter problem feeds into all sorts of other issues - global warming being foremost amongst them. If we had (for example) hydrogen fusion plants that worked - we could generate plenty of electricity with relatively little environmental impact - and use that to purify all the water we'll need. However, we don't have that energy - so we don't have the water. It's possible that there are other solutions to cleaning water - perhaps some nanotechnological filter. But until we have one of those things, saving water is therefore important. SteveBaker (talk) 03:47, 14 December 2008 (UTC)

Well, your answer is certainly in the spirit of the answers here SteveBaker; it still comes down to the quantity of availible, clean water, as opposed to total water. The ability (or lack there of) of us to provide that water is the reasons for water conservation. Your response certainly comes down to the economic factors over why water conservation is important, an aspect not fully explored, but it still comes down to the fact that, in the here and now, potable water is a limited resource in ALL of the world. It is more limited in some places than in others, but in no place is it so plentiful that there are no pressures to conserve it. The main crux of the debate seems to be between people who recognize the need to conserve water, and people who "can't be arsed" to alter their own comforts in order to conserve that water... --Jayron32.talk.contribs 03:55, 14 December 2008 (UTC)

Certainly for some places water is precious (some people live in the desert even in high society, Dubai, Las Vegas) but a lathe, for instance, which is the most common water using machine I would imagine used when making a car, is a highly efficient machine and does not have a waste water outlet so to imply that 1 million litres are wasted in producing a small engined car is not fair because it detracts from the areas people should be focusing on, whatever aeas they are. How long would you waste studying the lathe before you realised "Oh, it is as water efficient as can be since the early 1900s. The 1 million litres figure is basically irrelevant. I should have been looking at irrigation or something all the time." Cars waste petrol but not water. As for contaminating... water used in lathes is contaminated immediately with water based oil and all waste water is stuck on the waste metal therefore is burned up when recycling the metal and the only contamination should be a light smoke from that and whatever residue when cleaning the containers. Again about as efficient as conceivable, and I would like to believe that the oil used is not highly contaminating as I often had my hands covered in it all day, in a modern environment, making parts for stuff like a Harley and a boat. I had zero ill effects and would have to believe it to be somewhat moisturising (a watery milky blue oily stuff, no need for gloves). Machining metal is very similar to carpentry just more precise, not some chemistry job. ~ R.T.G 19:54, 14 December 2008 (UTC)

I'm not sure why you're stuck on lathes. If I were looking for water waste in the automotive industry, I would look first in the mining and processing of the raw materials. APL (talk) 19:18, 15 December 2008 (UTC)

Such a good point, I spent an hour or two on wiki to reference the water using in mining and refining iron and steel but found less than enough to even guess the quantities used in their production. Great point APL, spot on 100 points. There is a small book of info but almost zip about water sepecifics. Mining the iron seems to be by blasting but the seperation may or not be very wet. All things considered, 1 million litres of anything is a large amount to rinse off a couple of tonnes of ore. Enough to run a Honda 3000psi pressure washer for 60 days non stop which is a commercial strength concrete cleaning machine, a dangerous beast of a weapon that would cut you or strip paint off your car easy. ~ R.T.G 09:52, 16 December 2008 (UTC)

Question about Recursion

Background: On a Pet Milk can label, when I was a child, there was a picture that contained a picture of itself -- which suggests abstractly that the picture contains an infinte number of ever-smaller copies of itself. No graphic representation nor physical manifestation of this concept is possible, of course; but it is abstractly logical. QUESTION: What is the TERM for the underlying concept, in abstract mathematics, whereby an image may contain itself, such that it is rendered abstractly to be an infinitely iterative reductive series; and where would I find a source offering a rigorous mathematical treatment of this abstract concept? Gggiiillllll (talk) —Preceding undated comment was added at 19:29, 12 December 2008 (UTC).

Recursion, like in the title I just added for your question. Or, as you can see in the article, the Droste effect. Also, please sign your posts, using ~~~~. --LarryMac | Talk 19:36, 12 December 2008 (UTC)

Infinite regression might also be a topic of interest. -- 128.104.112.113 (talk) 19:41, 12 December 2008 (UTC)

Actually, there is a physical manifestation: The Infinite Cat Project! --Sean 20:53, 12 December 2008 (UTC)

Technically, 1601 is not quite infinite. It would have been neater if they'd arrange to take the last picture and paste it into a TV screen on the first cat page. SteveBaker (talk) 03:33, 14 December 2008 (UTC)

I'm very sorry, but you cannot understand recursion unless you understand recursion. -Arch dude (talk) 21:08, 12 December 2008 (UTC)

And - much more surprisingly - you can't fail to understand recursion unless you fail to understand recursion. SteveBaker (talk) 03:33, 14 December 2008 (UTC)

You also can't understand tautology without ... —Tamfang (talk) 09:18, 14 December 2008 (UTC)

I think the pertinent article is the Droste effect, and its cousin, mise en abyme. Follow the external link to Escher and the Droste Effect, and from there to The Mathematical Structure of Escher's Print Gallery.. - Nunh-huh 09:46, 13 December 2008 (UTC)

Also, fractal. —Preceding unsigned comment added by DanielLC (talk • contribs) 17:20, 13 December 2008 (UTC)

Man, user:SineBot's fast. I went back about five seconds later to sign that. — DanielLC 17:22, 13 December 2008 (UTC)

You can replace SineBot's signature with your own - no-one will notice (feel free to delete this message if you do)! --Tango (talk) 17:39, 13 December 2008 (UTC)

Pump type

Not sure if this question is "scientific" enough. If you think it should go in miscellaneous, plse. move it. I'm looking for a very low voltage pump (about 9V or thereabouts) to set up at a leak in our basement. I want to rig it so that it starts when there's water down there and turns off once most/all of it has been pumped off. The circuit is easy enough to whip up. I know that I need a suction pump, and one that can run dry for a while without getting ruined. That seems to rule out aquarium pumps. But I wouldn't know what to start looking for. Anyone a name for such an animal? (Finding how the water gets in seems to develop into a long term and costly project of elimination by trial and error. 2 possible causes down, no improvement, many more to go:-( 76.97.245.5 (talk) 20:51, 12 December 2008 (UTC)

Why 9 volts? Building centers/hardware stores have lots of utility pumps with water sensors which do this task. If the water contains dirt or mud or grit, it will quickly destroy pumps designed to pump clean water. Some aquarium pumps are rated to run dry for a time. A conductive sensor or float switch should be used to avoid the running dry problem. Maybe you could make a little dam around the leaking spot, out of Mortite or expanding foam or something to collect the water and make the mump's job easier. Hydraulic cement or other products could be used to fix the crack, rather than the fix proposed. Edison (talk) 20:58, 12 December 2008 (UTC)

http://www.google.com/search?hl=en&q=battery+powered+sump+pump&btnG=Google+Search -Arch dude (talk) 21:10, 12 December 2008 (UTC)

The water is seeping in along a wall, and maybe up through the foundation, not through any detectable crack. I've actually not yet caught it early enough in the process to find out more details. It only does that when we have one of those famed Georgia thunderstorm downpours, not when we get ordinary rain. We got a new roof, new gutters with gutter guards and the next step is going to be putting hydraulic cement and water barrier landscaping tarp along the sidewalk and wall on the outside. If that won't do, we'll have to get a drain pipe in the garden dug up and looked at. Failing that it get's real expensive with digging up the foundation form the outside and having it insulated. (People frequently get killed doing that unprofessionally, so we won't do that. which automatically means it'll cost oodles of money. I can't even get my hubby to understand why having water coming in through your wall and foundation is s.th. that needs to be remedied. He's not doing the wet-vacing.) Getting the water to collect at one spot would require more of an engineering effort than a quick fix would merit. I've put up a barrier along sections of the wall but some of it is under some built-ins. (more work -just what I need). I want the pump to suck up as much water as possible, so it's going to do an "last of the beverage through the straw" effect for a bit till the cut off doesn't have enough water for the circuit to close. I'll have a look at the sump pumps Arch dude linked. I hope they'll have some that are the right size. When I hear sump pump I think lots of flow, all liquid and dirt. What I need is little flow but no problem gargling up the silty water that comes in mixed with some air. My wet vac does that, but it's 120V and I don't want to mess with mains circuitry. Our electrical is my next project. (This Old House could have shows for ages in this place. It comes with a money drain.) Thanks for yall's help. 76.97.245.5 (talk) 23:08, 12 December 2008 (UTC)

Sump pumps like to have the water in a sump. If the water is of negligible depth, like a thin trickle, it is hard on a pump to sit there and basicall run dry much of the time. It should be possible to install a low dam a couple of inches inside the wall and catch all the trickles, and pump them out when the depth is half an inch or more down to perhaps 1/4 inch. If the depth is negligible, then a wetvac is the best solution. There are also absorbant rolls like the PIG which can be placed as a barrier, to catch occasional trickles. Another method is to have a contractor saw a groove in the floor an inch from the wall, which lets the water flow to an actual sump with a sump pump. Edison (talk) 20:48, 13 December 2008 (UTC)

Sump pumps are designed for situations like yours. They can detect water and turn on and off as needed. Beware that the water seeping through the walls will slowly erode them, however. StuRat (talk) 23:46, 13 December 2008 (UTC)

Thks. As I tried to point out earlier this is going to be a temporary quick fix while we are trying to find and fix the primary cause. (Such are notoriously hard to come by for infrequent basement leaks like ours.) I just don't want to come home to wet-vac duty or come downstairs a day or 2 after a midnight downpour to find that stuff that sat on the floor is soaked (again). Ordering a pump and doing a little tinkering I can always squeeze in, anything else that requires a contractor needs to be scheduled and for that we need to tackle the problem from the outside in. (In order to counter the erosion hazard StuRat mentioned.) Currently symptom relief will have to do, rather than a cure. 76.97.245.5 (talk) 07:09, 14 December 2008 (UTC)

Bilge pumps used in boats are just what you are after. Polypipe Wrangler (talk) 20:27, 19 December 2008 (UTC)

travertine

hello there i was just wondering if travertine is found in new zealand —Preceding unsigned comment added by 124.198.133.239 (talk) 21:56, 12 December 2008 (UTC)

Hi 124.198, you might find something in the Journal of Sedimentary Reseaerch, here[2] by going through the abstracts etc, but seems it could be connected to hot springs in the North Island. Julia Rossi (talk) 08:49, 13 December 2008 (UTC)

The only thing I could find except for someone claiming that their holiday pic showed travertine is the following: ...travertine deposits are common ... ."On the other hand, mixed silica-carbonate hot spring deposits are much more rare (Campbell et al., 2002). Among the best-studied silica-carbonate hot spring deposits, those from Waikite (Jones and Renaut, 1996; Jones et al., 2000b) and Ngatamariki (Campbell et al., 2002), New Zealand." This doesn't exactly rule out there is any travertine being deposited in those springs, either. Dendritic calcite crystals are reported to be a component of travertine. The former are found in hot springs at Waikite, North Island. You could maybe find more details with http://www.onegeology.org with another layer than the ordinary lithography. (That one only has things like "calcareous siltstone" and "limestone" so they may just not have travertine as a category.) 76.97.245.5 (talk) 18:03, 13 December 2008 (UTC)