Wikipedia:Reference desk/Archives/Science/2017 January 5

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January 5

AWG table, ampacity and voltage

Regarding the ampacity given in the table here: American_wire_gauge#Tables_of_AWG_wire_sizes - is this for the voltage 110 V AC or does it apply to any voltage (e.g. 230 V AC or 5 V DC?) --78.148.100.101 (talk) 05:21, 5 January 2017 (UTC)

In priciple, voltage is irrelevant when considering the current carrying capacity of a conductor. However, allowable voltages would be dependent on other factors, such as the insulation of the cable.--Phil Holmes (talk) 09:25, 5 January 2017 (UTC)

• (Edit conflict) You might be interested in our article on Ampacity. Ampacity is all about how much heat a wire can tolerate before it fails. Heating is a function of the power pumped into the wire, given by $P=I^{2}R$. Voltage doesn't come into play here (at least, not directly. Of course, increasing the voltage given a fixed resistance will increase the current). The ampactities in that table are for "Allowable ampacities of insulated conductors rated 0 through 2000 volts, 60°C through 90°C, not more than three current-carrying conductors in raceway, cable, or earth (directly buried) based on ambient temperature of 30°C". The skin effect will mean that a wire has slightly higher resistance to AC than DC, but if this Stack Exchange discussion is to be believed, that's not a problem - the cables are rated for AC, but if a cable meets AC standards it will easily meet the DC ones. Smurrayinchester 09:30, 5 January 2017 (UTC)

mean free path of a neutrino inside a neutron star

Is there an estimate available what the mean free path is for a neutrino inside a neutron star? Even if the mean frea path turns out to be very large, like much larger than the neutron star diameter, I'm wondering or hoping that it will be have been made small enough that a fraction of the many neutrinos passing thru will bounce around many many times, slowing down a bit, although i realize elastic collisions with heavier stuff don't give much slowdown for the lighter object. Thanks2602:306:CFC8:DDB0:31B7:1583:AFEC:841 (talk) 09:30, 5 January 2017 (UTC)

This [1] suggests 10s to 100s of meters depending on conditions, so definitely shorter than the ~10 km radius of a neutron star. Dragons flight (talk) 11:50, 5 January 2017 (UTC)

Interesting. I don't pretend to have worked the math, but if interaction dominates over absorption by v+n -> e+p, it sounds like this means there ought to be a reasonably large number of stationary neutrinos sitting at the center of a neutron star at a given time? If that star were then to hit something, like a sun, that slowed it down somewhat abruptly, could a fraction of these be released as a near stationary blob of neutrinos making its way through empty space? Would be a fascinating if absurdly unlikely scenario for watching the inhabitants of a hapless sci-fi world interact with the uninteractable... :) Wnt (talk) 12:49, 7 January 2017 (UTC)

China's nuclear stockpile as a deterrent

Considering China's nuclear capability and US defenses, would the US consider that, in the event of a nuclear war, some missles would land on US soil, and if so, how many and where, and would such a possibility serve as a deterrent? Anna Frodesiak (talk) 11:13, 5 January 2017 (UTC)

The United States national missile defense would not be entirely effective against a powerful country like China. As of early 2016, the US had ~30 interceptors capable of targeting incoming ICBMs. Depending on whose numbers you believe they each have an effectiveness of 25-60%, meaning the US could stop 8-18 incoming ICBMs at best. Most of China ~400-500 nuclear capable missile systems are regional in scale (see China and weapons of mass destruction), but US estimates that China has ~65 land and submarine based ICBMs that can reach the US directly. The largest ~20 of these have a MIRV capacity that allow them to carry 3-6 independent warheads each. So, if an all out war occurred today, China would be capable of destroying 40-100 US cities. That seems like a pretty good deterrent to me. Of course, both the number of interceptors and number of ICBMs could change over time or be subject to deliberate misinformation. Dragons flight (talk) 12:12, 5 January 2017 (UTC)

Axioms of the nuclear Deterrence theory called the MAD doctrine are that neither opponent could be expected or allowed to adequately defend itself against the other's nuclear missiles but each would retain overwhelming Second strike capability. The possibility of a smaller proportional response to "only" a few missile strikes does not enter this doctrine. Nuclear powers such as USA, Russia and China all operate submarines as an assurance of second strike capability after any Pre-emptive nuclear strike by another. The article China and weapons of mass destruction includes what is publically known about China's nuclear weapons. Blooteuth (talk) 12:35, 5 January 2017 (UTC)

40-100 US cities, eh? Okay, thank you kindly. Anna Frodesiak (talk) 06:09, 6 January 2017 (UTC)

White dog poop

Sorry to ask this, but I've wondered since I was a kid:

Why do I see white dog poop sometimes?

And don't say that is a stupid question that only I'd ask. I know there are lots of others out there who wonder too. :)

Anna Frodesiak (talk) 11:13, 5 January 2017 (UTC)

I thought the general consensus was that we don't see white dog poos much these days. I haven't seen a white dog poo for ages, or indeed much dog poo. Nowadays, most owners clean it up when their doggie does it's business in a public place. What comes in, affects what comes out - it's all down to diet. As a child, we used to feed our dog on scraps from the butcher, which contained lots of bones, and lots of raw meat. The calcium is what I suspect caused white poos. I think commercial dog food used to be made from whatever waste they could get from the abattoir, all minced up. Nowadays, maybe as a result of BSE, it's considered bad practice to use any old waste in dog food. From what I understand they no longer use all the offal and use more vegetable fillers. Growing up in Australia, in the 1960s, the only kangaroo meat that we ever saw was packaged as dog food. Now 'roo is served in the finest restaurants. PS I found this on youtube https://www.youtube.com/watch?v=8pIoR67ktSY --TrogWoolley (talk) 11:52, 5 January 2017 (UTC)

Personal observation, dog poo seems to "fossilize", sort of? It may be brown when the dog poos it, but later turns white, if it's left there for a while by an irresponsible owner, or buried but later dug up? Is this possible? Anna, was the white dog poo fresh, or old? Eliyohub (talk) 15:46, 5 January 2017 (UTC)

According to caninest.com: "Meat and bones used to comprise a large part of the domestic dogs diet, as a result their poop was rich in calcium. After a few days, water and organic components evaporated from their poop and what remained became dry, hard and turned white with calcium. Today’s dogs are fed from bags, tin cans and packets, with the occasional table scrap thrown in... Dogs these days rarely consume enough calcium to create the whitening effect on their poop". Alansplodge (talk) 17:19, 5 January 2017 (UTC)

So I was right, sort of? The "white poo" is only ever once the poo has dried? Eliyohub (talk) 21:34, 5 January 2017 (UTC)

Mostly. The feces can also come out white due to a lack of bile [2]. My bottle-kitten also had white stools for a week after we weaned her to wet kitten food. Never knew why, but she was otherwise healthy. Someguy1221 (talk) 04:56, 6 January 2017 (UTC)

I feed my dogs a raw diet. Raw chicken mostly though we get turkey around Thanksgiving. It has the meat, skin, and bone. (Yes, chicken bones can be eaten as long as they are uncooked.) My dogs have very light brown poops initially. After a couple hours, they start turning grayish brown and then eventually white. Once they are that color, they crumble apart when stepped on without sticking to my shoe. So, most of the time I don't mind stepping on them while mowing the lawn. †dismas†|^(talk) 05:01, 6 January 2017 (UTC)

Thank you all! You have solved one of the greatest mysteries in human history.

The following was transcribed from actual Egyptian tablets! I'm not making that up.

• Menkaure: ("Why is your dog's poo white?")

• Shepseskaf: ("Beats me. Probably nobody will know for thousands of years.")

• Menkaure: ("You know, Shepseskaf, you can't just leave that there.")

Seriously, thank you all. I've wondered for so long. By the way, I just posted about ash in cat food in case anyone is interested: Talk:Cat food#Ash in cat food. Best, Anna Frodesiak (talk) 06:05, 6 January 2017 (UTC)

You might also like to research the colour of spotted hyena droppings for extra information on why they are white.--Phil Holmes (talk) 09:52, 6 January 2017 (UTC)

I will, thank you, Phil Holmes. Anna Frodesiak (talk) 11:01, 6 January 2017 (UTC)

Curiously, white dog poo features in the study of social history, since the most unpleasant and degrading job described in Henry Mayhew's 1851 book London Labour and the London Poor, is that of the "pure-finder" or "dog-dung collector" who could sell dog poo at "from 8 d. to 10 d. per bucket" (about 4 new pence) because it was used in the leather tanning industry. It was mostly carried on by elderly women who were unfit for any other employment. "The 'dry limy-looking sort' fetches the highest price at some yards, as it is found to possess more of the alkaline, or purifying properties". [3] Alansplodge (talk) 16:51, 6 January 2017 (UTC)

So leather tanning already involving decomposing flesh, urine, and various toxic chemicals, and now we toss in dog poop to complete the bouquet. StuRat (talk) 17:09, 7 January 2017 (UTC)

What happened to Andrew Wakefield's co-authors?

In 1998 Andrew Wakefield and 12 co-authors published a paper in The Lancet, sensationally claiming a link between the MMR vaccine and autism (and bowel disease, but that didn't go down in history). The paper caused a major public health scare, but was shown to have dealt with data in a fraudulent manner and generally discredited. Andrew Wakefield was struck off from the UK medical register, and is no longer a qualified doctor.

What happened to the other 12 authors? Were they innocent and hoodwinked by Wakefield as well, or did they suffer similar fates? 212.240.171.198 (talk) 13:20, 5 January 2017 (UTC)

10 of the 12 co-authors published a retraction in 2004, saying the paper did not establish a link between MMR and autism. [4] I would guess that this was the end of the issue for those authors. The two others, John Linnell and Peter Harvey, later joined Wakefield in claiming that a potential link was still an important area of research [5]. Peter Harvey (a neurologist) died in 2012, and was praised by Wakefield as having stood by his convictions until his death [6]. As far as I know he never suffered any professional sanctions as a result of his involvement. The other author, John Linnell, is an obscure biochemical researcher. He seems to have left little public or academic footprint, and I have no idea what his current views on MMR are or if he suffered due to involvement with this paper. Dragons flight (talk) 14:04, 5 January 2017 (UTC)

Note that, as I understand it, from what you're saying, Linnell and Harvey simply spoke of a potential link as an important area of research - not claiming any convictions that such a link definitely existed, just that the possibility warranted further research. The only John Linnell scientist I could track down via google currently works for the Norwegian Institute for Nature Research. Probably not the same guy, but I don't know, but you can always email him via the institute and ask him. Possibly unrelated to the question, but I thought the issue under accusation was the preservative, not the vaccine itself, per se? Preservatives used in the vaccine have since been modified (necessarily or not, I can't comment) to address concerns, haven't they? Eliyohub (talk) 15:35, 5 January 2017 (UTC)

Thiomersal was the popular suspect, and was subsequently removed from, to my knowledge, all scheduled vaccines, whereas autism diagnosis rates have continued to rise. It is still used in some flu vaccines. The whole scare was really just a huge rabbit hole of terrible science, and you could write an entire article on how unfounded the theory is (which is why Wikipedia has several). Someguy1221 (talk) 04:11, 6 January 2017 (UTC)

Many thanks for the comprehensive answers, all. 212.240.171.198 (talk) 08:34, 6 January 2017 (UTC)

Lithium batteries - "dangerous to aviation"?

Recently, our ADSL internet broke down, so we called our communications provider. they sent us a cellphone to connect to the internet through, until they got their technician to come down to our property to fix the problem. Phone was sent by courier. As it happened, techie arrived fast (old cables had snapped at terminus and needed patching - not a hard job), so we never even opened the phone.

Now the company wants the phone back, perfectly fair. They sent us a self-addressed satchel to send the phone back via the postal service. The satchel is marked "ROAD TRANSPORT ONLY - NOT TO BE TRANSPORTED BY AIR". The explanation given is "contains dangerous goods (lithium battery) and must be transported in accordance with (relevant regulations on transport of dangerous goods)"

Now I DO know that Lithium is potentially flammable and explosive in certain circumstances. The most common issue is when it overheats. (A recent iphone release had this problem, I think? And maybe other cellphone designs as well). But how on earth is a battery in a switched off phone, or a battery that's not even in a device possibly be a danger to aviation? I know stuff transported on planes as cargo can get exposed to cold (cargo compartments are not heated), but I can't imagine any circumstances where it could be exposed to dangerous levels of heat!

When I've flown as a passenger, issues of taking my cellphone (or for that matter, notebook computers, which also often use lithium batteries) on the plane have never been raised. Never. Using the cellphone in flight is restricted under rules against radio interference (justified or otherwise), but this is a totally different concern.

So, is there any logic to this regulation which bans transport of lithium batteries by air in the postal service, as opposed to simply demanding that the battery be removed from the device (but included in the parcel separately) prior to posting? Is this some stupid "blanket" rule, assuming that people can't be trusted to follow other rules (i.e. remove the battery, and place it separately in the parcel)? Or is there some logic to this regulation? Eliyohub (talk) 15:32, 5 January 2017 (UTC)

Lithium battery has some comments, but might not fully answer your question. DMacks (talk) 15:49, 5 January 2017 (UTC)

Note the phone almost definitely has a lithium ion battery of some type not a lithium metal battery. Also from what be I've heard many flights do make a big deal about not trying to recover your phone yourself if it falls between the seats. Nil Einne (talk) 23:18, 5 January 2017 (UTC)

Of course, people cannot be trusted. There is a saying in the military that there is always a dumb*** who does not get a message. There are people who misinterpret or do not read instructions or forget, or too lazy, etc. --AboutFace 22 (talk) 15:53, 5 January 2017 (UTC)

Our article does indeed include info on the restrictions on carriage of Lithium batteries by air, but it says nothing in the way of expert opinion as to the actual safety need for the restrictions?

Also, can someone track down the IATA guidelines on the issue? They're mentioned in our article, but there's no link. Curious what they have to say about the matter, and whether they advocate a blanket ban on lithium batteries in the post. Found the document, honest, the rules sound extreme. Has there ever been an actual incident to justify them? Eliyohub (talk) 16:08, 5 January 2017 (UTC)

Read this. --Jayron32 16:21, 5 January 2017 (UTC)

(As well as the two crashes listed in that article, lithium batteries are also considered one of the possible culprits of the MH370 crash, which led to the restrictions being tightened. See Malaysia Airlines Flight 370#Cargo.) Smurrayinchester 16:27, 5 January 2017 (UTC)

Thanks, very useful articles. So the danger is real, but could be controlled if only batteries were safely packaged to avoid short circuits, and "device activation" in batteries in equipment (which can cause overheating risk)? Also, why don't planes carry fire extinguishers capable of extinguishing such a fire (the article you linked to says they don't), if the risk is real? (Obviously, I'm talking potential fires in the passenger compartment, not in the cargo hold). Eliyohub (talk) 16:30, 5 January 2017 (UTC)

Fire in the passenger compartment, not cargo hold. --Jayron32 16:32, 5 January 2017 (UTC)

Doesn't address my question - why no fire extinguishers on board of a type capable of dealing with this sort of fire, if the risk is real? If you have a particular type of fire risk aboard an aircraft (or anywhere else, for that matter), shouldn't you logically have appropriate fire-fighting equipment at hand? Fire extinguishers (even ones suitable for aircraft) hardly cost a fortune. (Also, as a secondary matter, it seems like a lot of the risk comes from faulty and poorly manufactured batteries more than anything else inherent in lithium batteries as a fire hazard). Eliyohub (talk) 16:38, 5 January 2017 (UTC)

Here is the U.S.'s FAA regulations regarding fire protection systems on aircraft. --Jayron32 17:38, 5 January 2017 (UTC)

Reading the document, you'd need "specialized dry powder" (usually a "copper powder" fire extinguisher, from some brief research) or at least sand, to fight what is clearly a "class D fire" (metals). It doesn't seem like aircraft are in fact required to carry such equipment. Given the "new" threat of lithium fires, does this need changing? Or at least in the interim, make aircraft carry a bucket of sand to smother the fire? (The latter won't work in all cases, but it would be a prudent and super-cheap stop-gap measure, if, for example, the burning phone or computer can be pushed to the floor - dump sand on it to smother it, because your standard fire extinguishers are useless). Has either (specialized "copper powder" fire extinguisher, or at least ordinary sand) been proposed as mandatory equipment to deal with this threat? As I said, sand would be easy and cheap to acquire and carry, imperfect as it is, it's clearly better than nothing? Would a Fire blanket work for this? Eliyohub (talk) 18:35, 5 January 2017 (UTC)

Your questions (like "does this need changing?") are not answerable in this forum. We're here to give you references. You're quite allowed to develop your own opinions (and don't even need to share them) and don't need us to give you your opinions for you. --Jayron32 18:51, 5 January 2017 (UTC)

Sorry, you are correct, this is not the place for opinions. It would be more productive to ask, 1) do airliners carry any equipment to deal with these types of fires? 2) My question "would a fire blanket work?" is clearly answerable. 3) And can you point me to any sources addressing this issue, and which include expert opinion on dealing with this threat, as far as lithium passenger cabin fires are concerned? Does all this fit within refdesk guidelines? No requests for your own opinions this time round. (I just emailed the FAA, curious what they'll say, if I get a response) Eliyohub (talk) 19:19, 5 January 2017 (UTC)

This article directly quotes FAA's recommended procedures for fighting those fires. It mentions there the use of specific types of fire extinguishers (such as Halon extinguishers and Halon-replacement extinguishers) to do so, This document describes the FAA's approved fire extinguishers for use on aircraft in the U.S., and Here is U.S. law that requires the maintenance of such extinguishers on all aircraft, it does not make exceptions for commercial airliners, so presumably such extinguishers are supposed to, by law and regulation, be available and maintained on commercial jets. --Jayron32 19:44, 5 January 2017 (UTC)

Important nitpick: those rules apply only to Part 135 operations, not to all aircraft; this is specified in 14 C.F.R. §135.1 Applicability ([7]) and 14 C.F.R. §135.141 Applicability (Subpart C - Aircraft and Equipment) ([8]). Most mortals do not fly on aircraft that operate under Part 135 rules - they can't afford to - so you're probably flying Part 121, "Air Carrier", when you fly on a commercial airline. A totally different set of stringent regulations pertain to Part 121 fire extinguisher equipment requirements (e.g. §121.308, §121.309(c)). To my knowledge, Part 91 operations do not explicitly mandate a fire extinguisher unless the official airplane paperwork lists such equipment as "required" for a particular aircraft or type. A few days ago, User:Dmcq mentioned that the super-rich are just like the rest of us - I bet he didn't realize they have special regulations for the special fire extinguishers they keep on their special jets!

During my private pilot examination, I flew a Citabria and complied with Part 91 operations rules; as required by the testing guidelines, my designated pilot examiner asked me "a question" during the "test section about safety equipment on board the aircraft" - today, that would be as specified in the new Airman Certification Standards IX. Emergency Operations Equipment and Survival Gear, but because we had no such safety equipment on board the aircraft, "the question" did not have anything to do with aviation. It was a spectacular example of the diligent care that one must exercise when reading the FARs. Treat the rules exactly as they are written, and do not attempt to interpret any more or any less.

For the record, these days I try to keep a fire extinguisher in the aircraft, irrespective of whether it is a regulatory requirement for my operations. It's a good thing to have in case somebody starts burning.

And to be extraordinarily clear, the FAA did actually send out a safety advisory specifically with respect to the Samsung Galaxy Note. I interpreted this safety order, FAA-2016-9288 Emergency Restriction / Prohibition Order, to apply to all air operations, including Part 91 and general aviation operations. WP:OR: Lithium batteries should scare you a lot more than they probably do. Because the fire is electrochemical in nature, and the battery provides both fuel and oxidizer, it is nearly impossible to extinguish a lithium battery fire using any type of fire extinguisher that is commonly available to firefighters and emergency responders. Source: the HAZMAT experts at the Sunnyvale Department of Public Safety, Fire Station #6, who I worked with during CERT training! This fire department is in the heart of Silicon Valley and is one of the best-equipped HAZMAT teams in our nation, and their advice to me, in case of lithium battery fire, was to clear out to a safe distance (reference your ERG guide for safe distance estimates) and just let the lithium burn out. If there is a fire inside an airplane, evacuation is frequently impractical.

I recently took another safety class on safe transport of lithium batteries, including compliance with IATA guidelines and UN Special Provision 188, and a bunch of other regulatory compliance stuff.... The rules have all gotten much more formalized as large organizations and governments are starting to apply the scientific method to understanding lithium battery hazard.

Perhaps later, when I have more time, I can provide extensive additional commentary on this issue, and on lithium batteries in general - I have lots of relevant and fun references! I bet in a few decades, we're going to look back on this part of our century and wonder how we could have ever justified this medieval use of this noxious material in so many consumer devices.

Nimur (talk) 01:40, 6 January 2017 (UTC)

For the record, I did look specifically for blankets. I can find no official process, procedure, or recommendation either for (or for that matter against) the use of fire blankets in fighting Li-ion battery fires, nor any studies as to their efficacy. --Jayron32 19:48, 5 January 2017 (UTC)

Thanks, those documents do clarify things. Your research is much appreciated, I learnt something new about fire-fighting. The FAA clearly is aware of the issue. Eliyohub (talk) 20:40, 5 January 2017 (UTC)

Re: the earlier point, I'm fairly sure class D extinguishers are not recommend for lithium ion battery fires http://batteryuniversity .com/learn/article/safety_concerns_with_li_ion [9]. They may be fine for lithium metal ones but these primary cells are rarer so although they have their own unique challenges, they don't get anywhere the attention as lithium ion batteries. In any case they have had stronger restrictions for longer. As I've now mentioned above, the phone almost definitely has a lithium ion battery. However if you were dealing with a lithium metal battery, while this is OR I'm not convinced putting a fire blanket on it is advisable. Such blankets mostly work by oxygen starvation but lithium metal battery fires aren't generally affected by (external) oxygen starvation [10] [11].

For lithium ion batteries it's more complicated, although they can generate their own oxidant [12] [13] (external) oxygen starvation does appear to help in some cases (see the earlier sources). Still from what I've read before, oxygen depletion isn't considered a great method for extinguishing lithium ion fires. Remember also, the greatest worry is thermal runaway affecting adjacent cells. If this is just a single phone, isolating it should stop that since phones generally only use one cell. If it's a laptop, it may have multiple cells, so I'm not sure covering it would be recommended. In any case, the available evidence suggests it's definitely not recommended over a suitable extinguisher, or putting the device in a container designed for that purpose and perhaps simply pouring water or some other cold non alcoholic beverage to try and cool it down and stop the spread [14]. There is some concern that people may try using water on lithium metal batteries which isn't generally recommended [15] [16] however this doesn't really seem to get much consideration on official advice, probably because as mentioned before the number of devices with lithium metal batteries is small. (Mostly you can tell by the device. Only with a few devices like torches is there a chance of either. And even then, if you can find the owner quickly you could always ask if it's rechargable.)

Definitely attempts to suppress fires during bulk transport are much more reliant on stopping thermal runaway see e.g. [17]. Note as mentioned in this source (somewhat sensationalist) but still [18], one of the big concerns other than the evidence showing how rapidly such fires may overwhelm the pilots, is that it appears the current suppression systems may not even completely stop such fires with bulk shipments.

Nil Einne (talk) 00:38, 6 January 2017 (UTC)

Indeed, Class D fire extinguishers are not recommended for lithium battery fires. The best response is evacuation, and in the event of exceptionally large (e.g. non-consumer) quantities of material, a lithium battery fire is a very serious HAZMAT situation that warrants specialist response, some guidance from the Department of Transportation includes the use of positive-pressure SCBA and at least a half-mile evacuation radius. Nimur (talk) 01:40, 6 January 2017 (UTC)

Regardless of whether or not people can be trusted, contrary to what the OP suggested, most guidelines for transporting lithium ion batteries recommend against removing them from devices. Actually, shipping lithium ion batteries outside devices is banned as cargo on passengers planes. Of course many devices can't have their batteries easily removed anyway. Nil Einne (talk) 23:25, 5 January 2017 (UTC)

When RoboSimian's lithium-ion batteries caught fire in June 2016, even the fine folks at NASA Jet Propulsion Laboratory's emergency response team could not extinguish the flame. The details of the event were published on NASA's intranet, and a few full-length videos of the post-accident analysis have been published to unofficial sources ...(Russians, apparently, have unrestricted access to these Federal computer systems). I find it instructive to watch the response from these highly-trained NASA Jet Propulsion Laboratory aerospace fire responders - ostensibly the most highly-trained, uniquely-capable responders who are very familiar with the hazards of unique chemical and physical substances in aerospace laboratories. Even with multiple types of firefighting equipment, the fire could not be extinguished.

Eventually, the lithium-ion battery was dragged to a safe area outdoors and was continuously cooled with water while the fire burned itself out.

Nimur (talk) 02:58, 6 January 2017 (UTC)

The two youtube links above are the same, but this shows the fire response. Part of the problem is they had a large, apparently heavy robot (notice how many times they fail to drag it) holding the lithium cells way up in the air. (The expense also has something to do with it - I imagine under other circumstances they might be handy with a fire axe) When you have hot lithium high in the air, I think obviously it's hard to exclude oxygen from the fire for a long time. I would guess that if they had happened to have an empty kiddie pool full of dry ice lying around, and could manage to flip the robot upside down into it, they might have had something ... not really standard fire fighting equipment though. :) Wnt (talk) 11:38, 6 January 2017 (UTC)

Thanks for that link, that's the presentation I was looking for! Evidently my URLs got crossed in an earlier post. Nimur (talk) 16:00, 6 January 2017 (UTC)

But as I mentioned above, external oxygen starvation is unlikely to completely extinguish a lithium ion thermal event. It may help a bit, but cooling it down and stopping it spreading to other cells (if applicable) is the more important thing. Nil Einne (talk) 11:48, 6 January 2017 (UTC)

Exactly. The fire triangle self-completes in a lithium battery fire - so extinguishers don't accomplish much at all. The responders then have to weigh the risk tradeoff between doing nothing, or adding large amounts of plain old water - that will cool the system, but will also encourage evolution of noxious gas including hydrogen fluoride and melted polymer fumes, as described in the NASA video. Yuck!

Fun fact: a regular lithium polymer battery, like the one you probably keep in your pocket, can burn underwater. When I was a little kid, these kinds of chemicals were heavily regulated hazardous materials that were only available to, like, Underwater Demolition Teams... now we have commercial advertisements encouraging regular people to swim with the same stuff strapped tightly to their bodies. Incredible!

Nimur (talk) 16:03, 6 January 2017 (UTC)

It's not as dangerous as a cesium battery. Count Iblis (talk) 22:18, 6 January 2017 (UTC)

Further reading:

• Astronauts Complete First of Two Power Upgrade Spacewalks, from Friday's post to NASA's official manned space flight blog, about the spacewalk on International Space Station to change some lithium-ion batteries outside the habitable part of the station
• How do you change a lithium ion battery in zero gravity? from Friday's issue of the Christian Science Monitor

Nimur (talk) 15:17, 7 January 2017 (UTC)

Why don't humans eat the pests on crops instead of spraying crops with pesticides?

Instead of spraying crops with pesticides or transplanting unusual genes into a plant genome to make the plant resistant to bugs, why can't humans just eat the bugs? Can humans just grow a large patch of grains, fruits, and vegetables without any pesticides and, if pests attack the crops, the pests will be collected and eaten (aphids, cockroaches, earthworms) and the surviving plants will be eaten or reproduce another generation of plants and then gradually the plants will become resistant to pests by artificial selection? Maybe the decaying fruits and vegetables and grains can be used to feed the worms in the worm farm, which generates organic fertilizer and some food supply in the form of worm meat. 66.213.29.17 (talk) 16:23, 5 January 2017 (UTC)

See Entomophagy#Cultural taboo. --Jayron32 16:29, 5 January 2017 (UTC)

More to it than that. In many cases, the number of pests vastly outstrips the ability of humans to pluck them off, even if the pests could have some theoretical value as food or whatever. "Chemical warfare" may be the only way to go. Larvae of Hypopta agavis are included in various Mezcals, but I do not think an Agave farmer would appreciate finding these creatures on his plants, despite them having some value. They damage the plants, and the plants are worth far more than these "worms", I imagine. Am I wrong? Eliyohub (talk) 16:34, 5 January 2017 (UTC)

• Humans do eat insects, but only large ones. We're just too big and clumsy to eat things at the aphid scale. Some pests are eaten - locusts are one. Nice big legs (in insect scale), well fed too. They're not a regular part of the diet because these pests occur in brief (but devastating) plagues and aren't available year round. Too much to catch rapidly and stop the plague, too infrequent to live on.

Worms aren't generally eaten. There's not much eating on a worm - much of their volume is a digestive tract, which has inedible contents and has to be left for a while to let their contents purge out first.

A better route might be to encourage pest predators, then eat those predators. Chickens would be a good example - they're famously good at de-pesting ground areas at the market gardening scale, looking for the sort of grubs that hide just below the soil surface. It's not unusual to run chickens over such a plot when the ground is fallow, and the manure helps too. Andy Dingley (talk) 16:37, 5 January 2017 (UTC)

We (i.e. humans) do eat many crop pests. One that springs to mind is corn smut aka Mexican truffle- absolutely delicious! Also locusts are commonly harvested and eaten in Africa and the middle east [19]. We also have an article on Kosher locust.

We already have lots of experience making plants resistant to pests via artificial selection, and that is the sole purpose of many commercial and non-profit endeavors, e.g. The_American_Chestnut_Foundation. We do have a whole article on plant breeding that is detailed and well sourced.

Most any good backyard gardeners or organic farm will be using plant scraps to fertilize, they call it compost and vermiculture.

Weeds are another crop pest that are sometimes eaten. Here [20] is a great resource on eating weeds, but I am not aware of any commercial endeavors.

Despite the fact that entomophagy is taboo to some, it is growing worldwide. The Food and Agriculture Organization has provided a great reference on the topic, including discussions of how entomophagy can be an important way to increase food security and feed security in the 21st century. I highly encourage anyone with a passing interest in entomophagy or food security to check out this wonderful reference on entomophagy, compiled by the world-class experts on the topic.

So, in short: sometimes we do eat pests, and many people are interested in eating more. You may also be interested in reading up on the related topics of integrated pest management, agroecosystems, and permaculture. SemanticMantis (talk) 17:17, 5 January 2017 (UTC)

Remaining passive to infestation by pests that by definition do damage to crops is a hopeless strategy. The infected crop should be razed and the ground disinfected to halt further growth of the pest. The idea of encouraging pests and artificially selecting surviving plants in the hope of breeding over many generations a plant that is both pest resistant and has not lost desirable qualities such as its taste, size and colour is a slow, haphazard approach to what today may be achieved by gene modification. In the US, by 2014, 94% of the planted area of soybeans, 96% of cotton and 93% of corn were Genetically modified crops. Blooteuth (talk) 17:20, 5 January 2017 (UTC)

I never said anything about encouraging pests, nor did OP. Please do not give your opinions here. "Hopeless", "slow" and "haphazard" are all opinions of yours, and we are not here to listen to what you think "should" be done. Mexican truffle is a clear example of something that is both a pest in some areas, and appreciated/welcomed in others. It does indeed damage corn. Some people raze it, some people eat it. If you want to cite references about pest management best practices for OP, I'm sure they'd appreciate it. SemanticMantis (talk) 17:27, 5 January 2017 (UTC)

The article Pest control documents a range of responses that include crop razing such as burning a sugar cane field after harvest to kill off any rodents, insects or eggs remaining, and destroying trees in a forest infected with insects. The OP asks about consequences of zero pest control effort in "Can humans just grow a large patch of grains, fruits, and vegetables without any pesticides....?". My comment is that to do so, especially when repeated over multiple generations in the gradual selective breeding program that the OP envisages, is to deliberately contribute to multiplication of the pest. Modern Agronomy is acutely aware of the Environmental impact of agriculture and how that might be affected by local "well meant" experiments. @SemanticMantis, your well referenced post emphasizes the Integrated pest management approach that aims to suppress pest populations below the economic injury level but you also make the point that certain crop pests are found to be edible, even delicious, and can therefore be valued as harvest, not pests, by those who enjoy them. May your enjoyment of mexican truffle be undiminished by poor tolerance of other informed opinions. Blooteuth (talk) 13:47, 6 January 2017 (UTC)

I am intolerant of all opinions on the ref desk, thank you very much :) I do appreciate that you are somewhat informed and also providing some references, but please avoid opining here. SemanticMantis (talk) 15:37, 6 January 2017 (UTC)

Another question is why we do not eat the crops, instead of using them for animal feed. Most of the corn and soy grown in the U.S. is used for animal feed rather than direct human consumption, which is a more expensive and environmentally damaging way to produce protein and calories. Another example is that the U.S. killed off the buffalo and used the land to raise cattle. Agribusiness has a vested interest in making expensive food, and obtaining government subsidies, and of course humans prefer meat to eating bugs. TFD (talk) 17:46, 5 January 2017 (UTC)

Well, if the vegetarian food is infested with insects, you can still feed it to animals. :) Seriously, the issue of whether ecological costs are fairly shown in the price of goods is a broad one - so long as people at the restaurant see similar prices for French Fries and Chicken Nuggets, they're not going to think that the meat could be particularly inefficient. And because of the frequency with which low-grade produce, silage, specialized crops for animal fodder and so forth are used, I'm feeling like one of those people. Wnt (talk) 11:51, 6 January 2017 (UTC)

In case of cheese this is done in Italy. Count Iblis (talk) 19:45, 5 January 2017 (UTC)

The OP might also want to look at Eating live animals#Invertebrates which includes a salad served with live ants. DrChrissy ^(talk) 20:49, 5 January 2017 (UTC)

There are many plants that are poisonous, and many insects that concentrate toxins from those plants. See lepidopterism for example... hmmm, that's a pretty incomplete article; even something like this is far better. Eating a known insect under known circumstances can be safe, but eating any random "bug" you come across, or even eating some potentially edible insects without knowing their provenance, is surely asking for trouble. Wnt (talk) 11:46, 6 January 2017 (UTC)

Locusts must have been on the menu in ancient times, see Leviticus 11:21-23: "Yet these you may eat among all the winged insects which walk on all fours: those which have above their feet jointed legs with which to jump on the earth. These of them you may eat: the locust in its kinds, and the devastating locust in its kinds, and the cricket in its kinds, and the grasshopper in its kinds. But all other winged insects which are four-footed are detestable to you..." Some translations have katydid instead of "devastating locust". Seems to be some confusion about the number of legs though... Alansplodge (talk) 17:02, 6 January 2017 (UTC)

Locusts have been on the menu in recent times (and probably still are). Certainly when my father was in Yemen in the 1950's, the local populace would readily grab locusts while walking through a swarm and munch on them. (Cue the Liverpool Kop End: "When you walk through a swarm, . . .") {The poster formerly known as 87.81.230.195} 2.122.62.241 (talk) 02:44, 7 January 2017 (UTC)

If humans die off from their own technologies, then can the planet recover from what humans leave behind?

Antibiotics are used liberally, and deadly antibiotic-resistant pathogens may arise from the livestock, which can jump to human populations. Machines are becoming smarter and more human-like. Greenhouse gas emissions are changing the climate. If humans die off from their own technologies and natural disasters finish off the rest, then can the planet recover from what humans leave behind? With so many greenhouse gases, will plants thrive in such a CO2-rich environment? Can wild animals' populations rebound and diversify? Will the oceans be stocked with sea creatures again? 66.213.29.17 (talk) 17:04, 5 January 2017 (UTC)

One important clarification. Plants love CO2, and grow faster with CO2 enrichment. It is basically fertilizer for plants. See any of the refs at Free-air Carbon dioxide enrichment, or I can supply more if you're interested.

A key article in this area is ecological resilience.

Most of the rest is WP:CRYSTAL territory. However, there has been plenty of speculation on the topic, and we can link to that, though we should not speculate here. One example is the TV series Life After People. SemanticMantis (talk) 17:22, 5 January 2017 (UTC)

(EC)Much of the modelling involved would involve speculation about certain variables, and perhaps others can point to sources. But let me say, as a general rule, that human impacts tend to have "winners", not just "losers". For example, the domestic cat is a big winner, with us humans willingly offering them abundant food and shelter, though in a post-human world, this may not last. Here in Australia, the Brushtail Possum equally has thrived in urban environments (much more than in its natural habitat), even if many humans consider it a pest. Global warming, too, will have winners as well as losers. Parts of now-frozen Siberia may well turn to flourishing forests. New Zealand, likewise, has been speculated to possibly be a "winner". (Low-lying island nations like Tuvalu may vanish underwater). Whilst areas of dense population today may well become largely uninabitable other than by creatures adapted to desert type environments. Maybe others can point to sources offering more specific models on potential outcomes? Eliyohub (talk) 17:24, 5 January 2017 (UTC)

There is a mini-series, The Future Is Wild, that speculates on what might happen. As Eliyohub points out, environmental change, while it can lead to mass extinctions, also benefits some groups. TFD (talk) 17:34, 5 January 2017 (UTC)

Also see extinction event for a wider view. --Cookatoo.ergo.ZooM (talk) 18:07, 5 January 2017 (UTC)

You could also take a look at the entries in the see-also section of the above-cited Life After People, including The World Without Us. Loraof (talk) 18:28, 5 January 2017 (UTC)

Life is always changing. Yes if humans disappeared you'd have an earth without humans. It seems you think of humans as a disease of the earth and inimical to life. On the contrary without some intelligence like ours life will die off on earth in the next couple of billion years. With us and our descendants it may spread throughout the galaxy in an enormous number of new forms. Dmcq (talk) 23:22, 5 January 2017 (UTC)

Why would the loss of humans cause the loss of life in general on Earth? I know of no reason why life in general would cease to exist on Earth in the absence of human life on Earth. Bus stop (talk) 23:30, 5 January 2017 (UTC)

If that's a reply to Dmcq, the answer is here. ("Couple" interpreted broadly, and noting the "like ours"). Henry^Flower 06:15, 6 January 2017 (UTC)

an aside on the validity of the question

I think OP is considering the notion that humanity may somehow cause so much general destruction, pollution and environmental degradation that the planet becomes inhospitable to all life as we know it. Essentially that we kill all ourselves AND take everything else with us. Not so much that we disappear tomorrow as what if we eke out a planet-destructive existence for several more centuries or millennia. Such a proposal may indeed seem unlikely, but it's certainly not conceptually impossible, it just takes a little imagination. Take some mix of runaway greenhouse gas, including massive storms and fires, burning all the forests destroying the ozone layer, bleaching all the coral, nuking all the pure water, salting the Earth, poisoning the air, etc., etc. Yes, life on Earth is resilient, but that does not mean it must go on no matter what we do. It's not an unreasonable to at least consider, and we can see above that there are many relevant references potentially available :) SemanticMantis (talk) 00:58, 6 January 2017 (UTC)

I just saw something about a similar CO2 excursion, probably from a comet, being responsible for the Paleocene–Eocene Thermal Maximum (our article makes it sound like just one theory, but the latest Science paper finding ejecta, which is mentioned way down in there, seems relatively persuasive). That event lasted for a few hundred thousand years. Antibiotic resistance is not "new" - the genes that mediate it have been around, and we have merely shifted the equilibrium, and in the absence of externally synthesized antibiotics it shifts back again. Now where Terminators are concerned, well, "Hey, just what you see here, pal." -- unless I see a self-replicating robot I can't comment on its ability to kill all future life. Wnt (talk) 11:57, 6 January 2017 (UTC)

Hmmm, come to think of it, that's the way it is sold in the news reports but this may be overly incautious. After all, we're talking about 55 million years ago. So I don't know if there could have been less methane on seafloors and in permafrost due to different bacteria or due to the lack of an ice age (though [21] suggests there was at least some glaciation in the late Thanetian). So extrapolating from that event to this one is probably a bit more like a guess or a hope than a monkey back guarantee. Wnt (talk) 12:24, 6 January 2017 (UTC)

I don't think life itself will have a problem with the damage we've done to the planet: experience of extreme environments and planetary history suggests some form of life will continue pretty much no matter what we do (see, for example, the radiation-loving radiotrophic fungus growing near the melted reactor core at Chernobyl), and over a long enough timescale, it will adapt. But individual species will be destroyed in great numbers, and the new ecosystems may well be radically different from the old. See this cartoon for context. Then, as is said above, in a few billion years, the increased power output of the Sun will end all life on Earth, and then later the Earth itself will be swallowed up into the Sun. And as Dmcq also says above, we might be able to spread life beyond the Earth, provided we don't screw ourselves. -- The Anome (talk) 12:32, 6 January 2017 (UTC)

Could an extant jet engine start on Mars without modification?

At ambient temperature and pressure. Mars' atmosphere has a small percent of combustibles. How much thrust would it make? 0.1%? 0? If it ignites what's the highest Martian elevation it could do so at? Sagittarian Milky Way (talk) 21:06, 5 January 2017 (UTC)

There is no way an "extant" jet engine would run on mars. A "JET ENGINE" typically refers to any internal combustion airbreathing jet engine. This is very different to a rocket engine, which can actually be referred to as a "non-airbreathing jet engine". For a jet engine to work it has to compress AIR which is used as the oxidizer in the "combustion" part, but the atmosphere on mars is 100 times thinner than on earth and is 95% carbon dioxide. I don't think that's anywhere near enough air or oxygen to get a jet engine going. Vespine (talk) 21:14, 5 January 2017 (UTC)

(edit conflict) The Martian atmosphere is 0.13% oxygen, compared with 21% on Earth. It's pressure is 0.6% that of Earth's atmosphere. The partial pressure of oxygen in Earth's atmosphere is about 21 kPa, while it is 0.78 Pa on Mars, or 0.00078 kPa. I really doubt a jet engine made to operate on Earth could even ignite. --OuroborosCobra (talk) 21:19, 5 January 2017 (UTC)

To put it another way, there is 27,000 times more oxygen in a sample of Earth's atmosphere than an equal volume sample of Mars' atmosphere. --OuroborosCobra (talk) 21:20, 5 January 2017 (UTC)

• While the point about lack of oxygen are correct, at the lowest parts of Mars (ie down in Hellas Planitia), pressure isn't that far off from jet engines being able to operate. It's about 11.5 millibars down there, or about 30 km altitude equivalent on Earth, according to the US Standard Atmosphere. Jet engines have gone higher than that (though I think only in zoom climbs). So if you were to supply oxygen to a highly efficient jet engine, it could work. Congratulations, you've now made the Mars equivalent of an air-augmented rocket. Fgf10 (talk) 21:29, 5 January 2017 (UTC)

Uhmm, Thinks to myself. Using the definition of jet, the Tupolev Tu-95LAL open cycle jet engine would provide thrust in a Martian atmosphere. If it were autonomous, the shielding would only need to protect the cybernetic electronics. --Aspro (talk) 21:42, 5 January 2017 (UTC)

What if you run the engine on hydrazine instead of jet fuel? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 02:34, 6 January 2017 (UTC)

It would then be a rocket and not a jet. As noted, in order to be a jet, properly, it needs to intake air. Please read the above again. --Jayron32 03:26, 6 January 2017 (UTC)

But hydrazine would burn just fine in Martian air, no? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 04:40, 6 January 2017 (UTC)

Nope. Hydrazine requires oxygen for a proper combustion reaction, and at partial pressures quite beyond what you see on Mars [22]. Hydrazine can be catalytically decomposed in an oxygen-free environment, but this doesn't seem suitable for a propulsion system, and still wouldn't be a jet [23]. Someguy1221 (talk) 04:50, 6 January 2017 (UTC)

Erm, monopropellant truster? You might want to tell hundreds of satellites with hydrazine thrusters they don't have a propulsion system. Not a jet as meant by the OP though, and not 'burning'. Fgf10 (talk) 08:16, 6 January 2017 (UTC)

Huh, no joking. I didn't realize the decomposition would be so...energetic. Thanks for the link. Someguy1221 (talk) 09:41, 6 January 2017 (UTC)

Wow, ethylene oxide is a monopropellant? Can you make a rocket that shoots out a continuous polyethylene glycol filament behind it? Wnt (talk) 12:29, 6 January 2017 (UTC)

See Solid-propellant rocket#Composite modified double base propellants. Yes, in short, although the glycol is used as a binder rather than being a combustion by-product. Tevildo (talk) 20:55, 6 January 2017 (UTC)

I wonder if a ramjet could work, on a rocket during entry into the Mars atmosphere, to provide just enough thrust to scout for a good landing position from close enough to the ground to see individual rocks. StuRat (talk) 03:52, 6 January 2017 (UTC)

The flight altitude record for a jet aircraft is about 135,000 feet, where it looks like the atmospheric pressure should be about the same as the mean martian surface pressure [24]. However, you still have 200-fold too little oxygen to drive the engine. Someguy1221 (talk) 04:04, 6 January 2017 (UTC)

Well copied from my answer!. Fgf10 (talk) 08:17, 6 January 2017 (UTC)

With a nuclear pile heating and expanding the intake air to turn and power the exhaust turbines (as in the Tupolev Tu-95LAL one doesn’t need oxygen -just a gaseous atmosphere. It is a jet. The air gets compressed, heated and then exhausted at a higher velocity to produce thrust and at the same time drive the compressor.--Aspro (talk) 18:09, 6 January 2017 (UTC)

Yeah but what was the tupolev engine flight ceiling? I actually doubt it was anywhere near as high as the altitude record for a jet engine, the regular tu-95 flight ceiling was just 45,000ft. The pressure up there is still far higher than anything found on mars. Vespine (talk) 22:52, 9 January 2017 (UTC)