Wikipedia:Reference desk/Archives/Science/2018 June 26

= June 26 =

Could all diesel engines use pure cetane if it's warm enough?
Are there cons besides wasting money and freezing at 18 Celsius? Sagittarian Milky Way (talk) 00:27, 26 June 2018 (UTC)
 * All "regular" fuel contains various fuel additives to impair engine wear and tear. So if you were to use pure anything as fuel, you'd beat up the engine. Apart from that, I believe you can use just about anything in a diesel engine as long as it will ignite under the conditions in the engine. --47.146.63.87 (talk) 07:05, 26 June 2018 (UTC)
 * Is there anything in Diesel engine which confirms what you believe? ←Baseball Bugs What's up, Doc? carrots→ 11:20, 26 June 2018 (UTC)


 * Almost certainly not. The highest grade of premium diesel fuel has a cetane index around 60. Pure cetane would ignite too early in the compression cycle, and would exert force that pushes backward against the engine. Looie496 (talk) 12:46, 26 June 2018 (UTC)
 * According to our article Since only air is compressed in a diesel engine, and fuel is not introduced into the cylinder until shortly before top dead centre (TDC), premature detonation is not a problem and compression ratios are much higher.
 * Beside that (and independently from what there is in Diesel engine) it is common knowledge that with some proper adjustment most diesel engine would run on almost everything, see e.g. http://www.uniteddiesel.co.uk/faq/can-a-diesel-engine-run-on-fuel-other-than-diesel and https://www.quora.com/Is-it-possible-to-make-motor-engines-which-can-run-on-both-petrol-and-diesel-at-the-same-time 194.174.76.21 (talk) 14:39, 26 June 2018 (UTC) Marco Pagliero Berlin
 * Does that "almost everything" include banana peels, for example? ←Baseball Bugs What's up, Doc? carrots→ 14:52, 26 June 2018 (UTC)
 * You could produce ethanol with the banana peal, and run on a ethanol-diesel blend. Doroletho (talk) 16:29, 26 June 2018 (UTC)
 * Good luck running today's diesel engines on (pure) ethanol.
 * Simplifying to the extreme: a diesel engine works by compressing air to high temperature/pressure, injecting fuel, and waiting for fuel auto-ignition and combustion. The cetane number basically is a measure of whether the fuel is easy or hard to auto-ignite.
 * The moment at which fuel is injected can be changed (I believe, but found no source to check, that it is changed in real time by the engine control unit in order to fix deviations in engine temperature or fuel composition), so that if you use a fuel that autoignites more rapidly you inject later to make up for the difference in delay, and keep the pressure peak at roughly the same "optimal" position (injection timing will change engine efficiency and pollutant production). In particular, cetane is always OK. However, if the fuel has a very long autoignition delay (e.g. ethanol), you can inject sooner, but thermodynamic conditions may not allow autoignition if you are too far from top dead center (temperature is high only when the piston is close to TDC). (For more mathy details about auto-ignition delays when temperature varies, a good search term is "Livengood-Wu integral").
 * TLDR - for diesel engine fuels, easier to ignite = better (all other things being equal). Tigraan Click here to contact me 08:41, 27 June 2018 (UTC)
 * So there would be no lubricity issues? How warm would the pure cetane have to be to not lower engine life by trying to force a too viscous liquid through a high pressure and tiny common rail fuel injector hole? Sagittarian Milky Way (talk) 18:01, 27 June 2018 (UTC)
 * Well, there could be, I have no idea. If you want to ask about lubricity of fuels, I would suggest opening a new thread. Tigraan Click here to contact me 14:21, 28 June 2018 (UTC)

Chicago Manual of Style: 1% vs 1 % ?
Does the Chicago Manual of Style dictate whether there should be space between a number and the percentage symbol? --129.215.47.59 (talk) 12:26, 26 June 2018 (UTC)
 * No space. See example and pointers to specific MoS rules at . DMacks (talk) 12:40, 26 June 2018 (UTC)


 * (ec) When in doubt about what the Chicago Manual of Style has to say, see the Chicago Manual of Style. TenOfAllTrades(talk) 12:48, 26 June 2018 (UTC)
 * Well, "see" if you or your affiliated institution has paid for it. That's why I went with a secondary but freely-accessible one. I'm not near a VPN-able machine right now, could you see what 10.52 and 10.61 are about (mentioned in the FAQ I linked)? DMacks (talk) 13:18, 26 June 2018 (UTC)
 * If you can't use a VPN, the Tor browser can do a lot of what you normally do with a VPN. --Guy Macon (talk) 00:01, 27 June 2018 (UTC)
 * Wut? DMacks was obviously talking about VPN-ing into their institution's credentials for the CMS. I doubt many Tor exit nodes have an institutional subscription. Tigraan Click here to contact me 14:24, 28 June 2018 (UTC)

I think the added space is an example of plenken, which is out of fashion nowadays. 173.228.123.166 (talk) 04:18, 1 July 2018 (UTC)

Determination of hydration number of ions
I see that the article Hydration number has a section titled Determination of .. where methods like NMR, neutron scattering and X-ray scattering are mentioned to involve radial distribution function, but some details about how the hydration number follows from those methods are missing. So I'd like to ask here how this quantity is derived from those methods? Which are the derivations steps? Thanks.--5.2.200.163 (talk) 15:46, 26 June 2018 (UTC)


 * These derivations are not trivial. You really have to go to the sources that are cited in that section to read how the derivation was performed for each method, and then each of those links to even earlier literature that explains how the equations they use were derived. Someguy1221 (talk) 20:26, 26 June 2018 (UTC)

NanoDrop ND-1000 from Thermo Scientific or Thermo-Fischer Scientific?
If I'm writing that I used a piece of equipment and want to put the manufacturer in parantheses but the company merged since the time of manufacture, changing from Thermo Scientific to Thermo-Fischer Scientific, do I write the old or current name of the company? 129.215.47.59 (talk) 17:46, 26 June 2018 (UTC)
 * Thermo Fisher Scientific is an American multinational biotechnology product development company, created in 2006 by the merger of Thermo Electron and Fisher Scientific, and currently owns the brand NanoDrop . Giving the current name of the company will be more useful to a reader seeking further information. DroneB (talk) 19:18, 26 June 2018 (UTC)

The Biology of Human Starvation
Where can I download the full text of "The Biology of Human Starvation" by Ancel Keys from 1950? Thanks for your help. — Preceding unsigned comment added by 180.183.85.18 (talk • contribs)
 * The book is not in the public domain, so downloading it would be book piracy, which is illegal for most users on this site. Ian.thomson (talk) 18:11, 26 June 2018 (UTC)
 * According to Google Books there is no electronic version of this text available. Your best bet would be to find a library on WorldCat that carries it. It can be found in many university libraries. Someguy1221 (talk) 20:17, 26 June 2018 (UTC)


 * I recently needed to refer to a book. It was cheaper and far less hassle to just order a used one from Amazon than it would have been to try to get it via inter-library loan. -Arch dude (talk)

What is this and should I be worried?
I have a large stand of alders on my property that are just coming to maturity after a decade or so. In the last week I’ve seen these weird yellow spots on some of them. It doesn’t looks like anything good, but I don’t know if there is anything I cnan or should try to do about it. Beeblebrox (talk) 22:18, 26 June 2018 (UTC)


 * Perhaps Phytophthora alni? Count Iblis (talk) 22:37, 26 June 2018 (UTC)
 * Doesn't look like that to me, my thought was an insect laying eggs. Would it be possible to get some more close up pictures, and of the reverse of the leaf as well? DuncanHill (talk) 22:42, 26 June 2018 (UTC)


 * I think they are alder leaf galls, perhaps caused by Eriophyes inangulis. (You can find pictures online that look a lot more like yours than the ones in our article, for example https://www.alamy.com/stock-photo-a-leaf-gall-caused-by-the-mite-eriophyes-laevis-on-alder-leaves-dorset-20563260.html.) Looie496 (talk) 22:57, 26 June 2018 (UTC)
 * I think that’s pretty likely, it looks a lot like some of those images. Sounds harmless so that’s a relief. Beeblebrox (talk) 00:37, 27 June 2018 (UTC)

Effects on refrigerated food of exposure to ozone
What are the effects on refrigerated food of exposure to ozone? I ask because a well-known brand of refrigerator advertises itself with the claim "Active Oxygen removes bad smells, such as strong cheeses, and keeps bacteria at bay to keep your food fresher for longer. Active Oxygen technology releases tri-oxygen molecules (O3) into the fridge, which neutralises unpleasant odours and helps prevent bacteria growth by oxidising it away. Active Oxygen is a molecule made up of 3 oxygen atoms – the same type that are present in nature and released into the atmosphere during a thunderstorm. Active Oxygen technology recreates this process inside your machine, so it doesn't need any refilling or maintenance." I'm not sure I'd want a lungful of ozone every time I made a cup of tea, but that's another matter. DuncanHill (talk) 23:48, 26 June 2018 (UTC)
 * That would depend on the concentration of ozone in the air volume within the refrigerator. At low concentrations, it would only react with the surfaces of food items. Ozone can in theory degrade nutrients (especially anti-oxidants) in the food items by oxidising them, so you wouldn't want the ozone to penetrate too deeply beyond the surfaces of food items. When ozone reacts, it generates regular, harmless oxygen in the process. If the concentration is significant, you could be damaging your health in the long term from the cummulative effect of repeatedly inhalling ozone everytime you open the refrigerator door. I can't say for sure whether any of these things are worth worrying about, as I don't know the concentration involved here. Plasmic Physics (talk) 00:55, 27 June 2018 (UTC)
 * Seems like a combination of uselessness and danger; you don't want to be inhaling ozone on a regular basis - see Ozone. Maybe they should instead come up with a way to displace the oxygen in the fridge with nitrogen and reduce spoilage that way. Matt Deres (talk) 12:50, 27 June 2018 (UTC)
 * "don't want to be inhaling ozone on a regular basis." Yes, but remark that you (and the most of us) are repeatedly inhaling much more ozone everytime you come near a working laser printer or UV lamp and when you go in the sun out of your home, especially but not exclusively at the seaside and in the mountains.
 * Beside that you could balance the hazards of breathing some ozone today against the danger in twenty years of getting a liver cancer from some unseen trace of mold growing on your lettuce. 194.174.76.21 (talk) 17:07, 28 June 2018 (UTC) Marco Pagliero Berlin
 * The bit about the "seaside" sounds like a remnant of an old folk idea that ozone was somehow good for you. The main exposure to ozone, as I understand it, is from photochemical smog, and you're likely to get much more of it in the city where there are lots of cars (or sometimes in outlying areas that happen to be downwind of cities with lots of cars, especially if there's a mountain range for the smog to back up against). --Trovatore (talk) 18:49, 28 June 2018 (UTC)
 * That said &mdash; what matters is the numbers. No one has reported the actual concentration of ozone in this fridge, so it's impossible to say whether it has health implications or not.  I can imagine a scenario where you just hold your breath when you actually open the fridge itself, and the concentration of ozone leaked into your living space is too small to matter, but that's pure speculation until we see some numbers. --Trovatore (talk) 18:56, 28 June 2018 (UTC)


 * Numbers, please, we need numbers.
 * According to Air quality index, air is "Unhealthy" if the ozone concentration exceeds 86 ppb for eight hours, or 165 ppb for one hour. I guess most subway rides are less than an hour, but still, this should give a sense of the range of values involved. --Trovatore (talk) 19:36, 29 June 2018 (UTC)
 * The A train is 2 hours (a fairly inland part of the city to full ocean beyond all harbors, circuitously). There's quite a number over 1 hour in this city alone but they're generally just edge to CBD to edge which isn't surprising since an hour's a common commute willingness limit. Sagittarian Milky Way (talk) 22:21, 29 June 2018 (UTC)
 * Here is an interesting note from the ozone article:
 * In the Victorian era, one British folk myth held that the smell of the sea was caused by ozone. In fact, the characteristic "smell of the sea" is caused by dimethyl sulfide, a chemical generated by phytoplankton. Victorian British folk considered the resulting smell "bracing".
 * I wonder if that's where Marco got the idea about the "seaside". --Trovatore (talk) 20:44, 29 June 2018 (UTC)
 * Hence the neighbourhoods Ozone Park and South Ozone Park, designed to entice settlers with just the contact high of being kilometers from the ozone, and second-hand ozone from the sea breeze or something. Sagittarian Milky Way (talk) 23:48, 29 June 2018 (UTC)