Wikipedia:Reference desk/Archives/Science/2016 February 28

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February 28

Gigameters

I see that all the usages of astronomical distances when using SI multiple of meters is in kilometers, most commonly in millions. Why don't gigameters be commonly used instead, it's the one-word unit for millions of km? Earth's distance from the Sun is 149.6 Gm, which is the same as 149.6 million km. Whether gigameters should be referred instead of millions of km would be up to astronomers. I can see this unit will eventually be adopted for common astronomical use. PlanetStar 02:18, 28 February 2016 (UTC)

Because 96 million miles (billion paces) is far better, as is even one AU? Long live Boris Johnson! μηδείς (talk) 02:34, 28 February 2016 (UTC)

Astronomers don't even seem to have fully embraced the metric system, using astronomical units and light-years instead, for distance, and solar masses for mass. StuRat (talk) 04:08, 28 February 2016 (UTC)

Don't forget the parsec (3.0857×10¹⁶ m) - based on AU of course. Mikenorton (talk) 10:37, 28 February 2016 (UTC)

And it's also worth noting that, even when using metric, astrophysicists still use CGS rather than SI units, so the Sun is described as radiating 4 * 10^33 erg / sec... Tevildo (talk) 11:41, 28 February 2016 (UTC)

It depends on context. On Orbits for station and satelites kilometers or miles are used. In our Solar System and the nearest systems you will usually see AU and everything beyond is usually measured in lightyears. Also there is Parsec since 1913. Astronomers dont care that much about standards i guess. --Kharon (talk) 03:04, 29 February 2016 (UTC)

Lots of fields have occasional departures from strict SI conformity. For example concentrations of gases often are expressed in parts per million, temperatures in degrees Celsius and so on. Shock Brigade Harvester Boris (talk) 03:13, 29 February 2016 (UTC)

Pregnant pilot

Suppose an aviatrix who regularly flies unpressurized aircraft (such as those used in air taxi operations) was to become pregnant -- how would this affect her ability to withstand mild-to-moderate hypoxia (such as that caused by flying at altitudes from 8,000 to 12,500 feet (and up to 14,000 for short periods when necessary) without pressurization)? Would she have to stay below 10,000 feet or below a still lower altitude for the next 9 months? (NOT INTENDED AS MEDICAL ADVICE) 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 02:31, 28 February 2016 (UTC)

Some things that can influence the outcome: She makes up 50% more blood than before she got pregnant. I assume that would help. A fetus already has to deal with low oxygen, so low oxygen in the mother might be really bad. But then again a fetus makes Fetal hemoglobin which might help. Maybe look into advice give to mountain climbers - there are people who routinely live at such altitudes. See: High-altitude adaptation in humans Ariel. (talk) 02:39, 28 February 2016 (UTC)

That article is about evolutionary adaptation to high altitudes (as seen in Sherpas and such), not regular mountain climbers. Perhaps the word we should be looking for is acclimatization? 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 02:47, 28 February 2016 (UTC)

The FAA's published list of resources for special medical and health topics lists research on the effects of In-Flight Radiation Exposure During Pregnancy; and this unfortunately grisly research paper on Impact Injuries During Pregnancy: Experimental Studies (1968); but I can find nothing about health effects of hypoxia during pregnancy.

WP:OR: I have flown with at least one pregnant flight instructor; and I do specifically recall that she mentioned greater concern about exposing herself to radiation from a nearby RADAR facility than from hypoxia (...or from demonstrating engine-out procedures in a single-engine rotorcraft -- twice). That might give you perspective, anecdotally, on at least one informed individual's assessment of relative risk. In fairness, the particular RADAR at issue is particularly spooky, so I don't fault anyone, pregnant or otherwise, who wishes to remain on the right side of its RADAR equation...

If you carefully read the FARs, 12,500' and 14,000' are threshold altitudes for required use of oxygen (14 CFR § 91.211); but I know plenty of aviators who prefer to start sucking air out of a hose at much lower altitudes. In fact, the PHAK provides advice (§6-34) on the use of supplemental oxygen even if it is not legally required for the flight crew or passengers.

Nimur (talk) 03:58, 28 February 2016 (UTC)

So I gather that any added hazard from hypoxia would be slight to negligible, right? Thanks! (BTW, that's one brave lady to teach autorotation procedures to new pilots.) 2601:646:8E01:515D:F88D:DE34:7772:8E5B (talk) 06:56, 28 February 2016 (UTC)

Eh? How are you gathering that? Everyone just said "use oxygen even when not pregnant", how do you go from there to "no danger"? Ariel. (talk) 07:04, 28 February 2016 (UTC)

One doctoral dissertation found small behavioral changes in rat pups as a result of the pregnant rat being repeatedly exposed to low pressure similar to airline flight. See "Prenatal influence of slight variations in altitude: Hypoxia and maternal influences on offspring ," by Charles Arthur Graessle, 1978. Edison (talk) 15:28, 28 February 2016 (UTC)

A summary of this experiment was published in Bulletin of the Psychonomic Society, 1978, Vol 12 (4), 329-331, "Effects of mild prenatal decompressionson growth and behavior in the rat." The pups whose mother was subjected to the 6000 foot altitude had pups of lower weight and were less mobile. There were negative behavioral and psysiological effects from the mild decompression. It could not be ruled out that the effects were mediated through the mother's health or behavior as opposed to effects directly on the pups. See [1] Edison (talk) 20:54, 28 February 2016 (UTC)

Hypoxia is only one of many physiological factors to consider.

Any aviator must make an informed decision about risk before flying; in the unique case of pregnancy, some aspects of risk might change. The best way to inform such decisions is probably to talk to both a regular pre-natal care physician (e.g. an obstetrician) and to an AME or similar medical doctor with aviation expertise. Every (legal) pilot in the United States has to visit an AME every once in a while, anyway ... so that right there is a great opportunity to ask questions! Anybody who takes aviation health (or child-birth) seriously will want to spend a little real-world effort to get a more well-rounded answer than we can possibly provide here.

After scouring for more sources, I found this 1994 brief from Army Aeromedical Research Lab: Tech Report 94-44, Pregnancy and Flying Duties. Here is a Navy aviation document that also contains the same advice: consult a flight surgeon and a pre-natal care physician. That last paper details a lot of the unique physiological changes associated with pregnancy: blood sugar, dehydration, and other concerns. There is also a paragraph on health and policy for hypoxia. Per Navy policy, pregnant Navy aviators appear to be restricted to flights at cabin-pressure lower than 10,000 feet. (Navy aviation rules are sometimes quite different from civil aviation rules, for many reasons). Interestingly, these military aviation resources go to great lengths to emphasize that pregnancy is considerd a normal health condition, and although it has uniqueness, it is not an abnormal health condition. In itself, normal pregnancy (without any other health complication) does not preclude flight duty.

I also found this snippet in FAA's textbook, Introduction to Aviation Physiology. That book contains the phrase - direct quote - "It has also been determined that pregnancy is not compatible with flying because of the possible effects of G-forces, mild hypoxia, and other stresses associated with the flying environment." This statement is ... well, "not compatible" with the many other references I have linked, including resources from FAA and military aviation sources. I would go so far as to say that it merits writing a letter or email to the FAA Civil Aerospace Medical Institute to ask them to review and update their aviation physiology reference text. That statement is very outdated and does not really jive with the rest of the reading I've done. Their correspondence address is listed on the first page.

Nimur (talk) 23:31, 28 February 2016 (UTC)

So, up to 10,000 feet is safe, but anything higher than that (without oxygen) risks complications? Thanks! 2601:646:8E01:515D:986D:7DB1:2770:DAA7 (talk) 06:21, 29 February 2016 (UTC)

No; that's not the way I would summarize it; I would say most sources recommend discussing the medical facts and risks with at least two highly-specialized medical professionals, but most rules leave the ultimate decision-making about how to deal with risk to the pilot in command. That's entirely different than concluding that some course of action carries "no risk."

Nimur (talk) 16:22, 29 February 2016 (UTC)

Unreferenced noise. AllBestFaith (talk) 15:29, 29 February 2016 (UTC)
The following discussion has been closed. Please do not modify it.
I think the real worry here is that the lower pressure might vacuum out the baby midflight. μηδείς (talk) 22:00, 28 February 2016 (UTC) That's a particularly crass, rude, and unencyclopedic thing to say. Maybe you ought to spend more time reading references before posting responses? Nimur (talk) 23:19, 28 February 2016 (UTC) It's called a joke. (BTW, the term is "jibe with" in case "jive" was not inadvertent on your part.) I don't need to be lectured on anatomy or your particular PC belief system. The question was already asked and answered. μηδείς (talk) 03:45, 29 February 2016 (UTC) It is not appropriate to level personal attacks on editors in front of the OP. ←Baseball Bugs What's up, Doc? carrots→ 05:30, 29 February 2016 (UTC) small for jokes? Dbfirs 10:38, 29 February 2016 (UTC) You're right, Nimur forgot to add a smiley and/or put it in small print. ←Baseball Bugs What's up, Doc? carrots→ 12:12, 29 February 2016 (UTC)

If you make an organolithium reagent by reacting lithium metal with alkyl halide, wouldn't the generated organolithium reagent also react with the original alkyl halide?

It's a thought that I didn't seem to have when learning orgo, or didn't seem to have to know, but now that I'm actually tutoring it during the evenings (while my current day career path is in biochemistry and it currently looks like I will never ever have to make an organolithium reagent in my life), this thought is kind of killing me. Is the SN2 reaction just much slower than the lithiation (organolithium reagent formation) reaction? Yanping Nora Soong (talk) 08:03, 28 February 2016 (UTC)

By overwhelming empirical evidence, the SN2 reaction is much slower than the radical reduction in practice, else the lithiation wouldn't be considered as a usable reaction. Order of addition and solvent play a big role. DMacks (talk) 09:44, 28 February 2016 (UTC)

Can you help me find the sources on the order of magnitude differences involved? (This is to inform my students.) For example, am I correct to guess that perhaps, the lithiation reaction might be over in seconds or minutes to complete (on a laboratory scale) but the SN2 reaction would take several hours or fractions of a day? Yanping Nora Soong (talk) 13:29, 29 February 2016 (UTC)

Why do I don't find an article about endocrine cell - on Wiki?

Is it under other name or it's not accepted term? 93.126.95.68 (talk) 14:01, 28 February 2016 (UTC)

The endocrine system involves a number of different types of cells, with not much in common, so the generalized concept of an "endocrine cell" is probably of little use. The tables in our article Endocrine system include a column headed "From cells", from which you can follow links to the specific types of cells responsible for various hormones. Deor (talk) 14:13, 28 February 2016 (UTC)

I agree, but I just created Endocrine cell as a redirect, since it is clearly something that at least one person was searching for. Looie496 (talk) 14:33, 28 February 2016 (UTC)

A simple search reveals that "endocrine cell" is a term used (for instance, a paper asking "is an adipocyte an endocrine cell?"). At a very high level of abstraction, I would think a cell isn't endocrine or exocrine per se, because it is the geometry of how the cells are connected that determine whether the secretion escapes to an internal or external body surface. But in reality exocrine cells must be designed to contact some part of the "outside" of the body (such as a lumen, as in the intestine or salivary gland) have an apical surface with certain specialized methods of secretion. And whether a molecule that is retained in the body is considered an endocrine secretion depends on the molecule and its activity and whether it can travel in the circulation, and thus a cell that makes those molecules (assuming that they wouldn't somehow all be excreted) is indeed an endocrine cell, such as a pancreatic beta cell. Wnt (talk) 15:30, 28 February 2016 (UTC)

Evaporation

If I have 2 liters of liquid poison, evaporate the water off and collect it via condensation in a sterile beaker, would it be safe to drink? — Preceding unsigned comment added by Mugimuimue (talk • contribs) 18:01, 28 February 2016 (UTC)

Name your poison! Exactly what happens will depend on just what is dissolved in the water. You might have pure water - or you might still have poison, depending on whether the poison evaporates at or near the temperature that water evaporates. — Preceding unsigned comment added by 109.150.174.93 (talk) 18:14, 28 February 2016 (UTC)

(EC) Maybe, maybe not. What's a poison in general? What type of poison are you thinking about for this thought experiment, and how does it react with water? Does it make an azeotrope? The LD50 of ethanol is about ethanol is 7g/kg [2].

My point is that the dose makes the poison, and something like wine could be considered a poison (and certainly fits our definition), and by collecting the condensation (effectively slowly distilling) you'd be increasing the toxicity of the poison. You might be interested in reading up on fractional distillation and partial melting, which are two general processes relevant to the question. SemanticMantis (talk) 18:17, 28 February 2016 (UTC)

I think the OP meant drinking the evaporated-off water, not the remaining poison! In case the OP doesn't manage to distill the appropriate information from SemanticMantis's very relevantly linked articles, I'll summarize by saying that evaporation/distillation can almost never produce an absolute separation of mixed liquids in one pass; repeated re-distillations (or evaporations) would be needed in order to bring the poisonous fraction below an acceptable threshold, but what that threshold would be and how many iterations would achieve it is likely not easily calculable even if the substances and conditions are specified. In fact, acceptable separation might not even be possible, and additional different methods might have to be applied. Don't try this at home! {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 15:26, 29 February 2016 (UTC)

Hm, I meant that the condensed evaporate could have higher toxicity than what you started with. Maybe I'm wrong, but I thought that you could in principle run a still very slowly at ambient temperatures, in which case the distillate has higher ethanol concentration, and is hence more poisonous. Stills work because ethanol boils at lower temp than water, but doesn't that mean more ethanol than water also evaporates at room temp? I could be wrong about that, anyone want to help me out? Can a room-temperature still serve to slowly increase the proportion of ethanol in a water/ethanol mix? SemanticMantis (talk) 16:27, 29 February 2016 (UTC)

Does anyone know if the OP is still alive? He hasn't posted since yesterday. This should probably be refered as a threat of self-harm to the Wikimedia foundation, should it not? μηδείς (talk) 22:02, 29 February 2016 (UTC)

@Medeis: surely you are joking? If not, report as you see fit. If so, I don't think our guidelines, ethics of reporting, and self-harm are very good topics for jokes, especially in a text-only channel where humor often gets misconstrued. SemanticMantis (talk) 16:46, 2 March 2016 (UTC)

Well, no. This question is the user's sole contribution to wikipedia. They have asked about drinking poison after evaporating off the water. If you wish to see me as the problem here, then report me to the wikimedia foundation. μηδείς (talk) 18:59, 2 March 2016 (UTC)

Growing

If I put an ivy cutting into a glass of water, the cutting grows and gets bigger and longer. Explain to me how it's mass can increase from nothing but sunlight? — Preceding unsigned comment added by MrBeansInMyPants (talk • contribs) 21:51, 28 February 2016 (UTC)

See Photosynthesis. The plant takes carbon dioxide from the air and combines it with the water. The sunlight provides the energy. Tevildo (talk) 21:58, 28 February 2016 (UTC)

And a question asked by Jan Baptist van Helmont 450 or so years ago. --Tagishsimon (talk) 22:10, 28 February 2016 (UTC)

This is related to Conservation_of_mass, that article isn't fantastic in my opinion. Now if THAT is blowing your mind, check THIS out: Say you have a big air tight tank, like the size of a block of apartments, then you put a big tree in it that weighs one ton. and you seal it up and weigh the whole thing. Now you burn the tree so that you are left with nothing but some ashes. The whole tank will still weigh exactly the same amount! The mass of the original tree will equal the increase in mass of the "air" (the additional carbon dioxide) plus the remaining ashes. Vespine (talk) 00:37, 29 February 2016 (UTC)

About half the dry-weight of any plant is carbon [3]. I don't know what kind of ivy you might mean, but Epipremnum_aureum is a liana commonly grown indoors in water, and it has about 90% of its living weight as water. SemanticMantis (talk) 14:29, 29 February 2016 (UTC)

• In order to grow a plant needs carbon, hydrogen, oxygen, nitrogen, phosphorus, and potassium -- other elements usually only in small quantities. Carbon comes from CO2 in the atmosphere, via photosynthesis. Hydrogen comes from water. Oxygen comes from air and water. Nitrogen is usually taken up by the roots, although some plants can extract it from air with an assist from symbiotic bacteria. Phosphorus and potassium need to be taken up by the roots. Thus the main things a plant needs to get from its roots are nitrogen, phosphorus, and potassium -- these are the primary ingredients in fertilizers. A plant grown in pure water won't get them, and therefore won't continue to grow for very long -- it can only make use of the amount of them it has stored. But because the great bulk of a plant is made up of carbon, hydrogen, and oxygen, it can sometimes grow substantially before it runs out of steam. Looie496 (talk) 15:03, 29 February 2016 (UTC)

Plant uptake and allocation of nutrients is a deep and mysterious topic. Nitrogen_assimilation is curerntly very limited, and only discusses roots. Retranslocation helps [4]. Many plants can take in NPK through leaves, flowers, and other non-root tissues. Foliar feeding and other related mechanism allow plants to get nutrients from dust/debris/air/etc. I've had plants in water for many years that still manage to visibly grow. SemanticMantis (talk) 16:22, 29 February 2016 (UTC)

Note that plants can't absorb nitrogen gas, either from the air or dissolved in water. They take in nitrogen based salts (primarily nitrides, nitrates and ammonium). Legumes (peas, beans et al) have bacteria in their roots that can fix nitrogen gas, and carnivorous plants take nitrogen and other minerals from animals. LongHairedFop (talk) 20:35, 29 February 2016 (UTC)

Is there an "app" for signaling when something in the freezer starts freezing?

This sounds pretty dumb, but you know how people put bottle of champagne in the freezer just to get it a bit colder and then forget about it and then it freezes? Of course the freezer manufacturers could install a button and sensor or timer, but barring that, is there one on apple etc?97.117.106.130 (talk) 22:21, 28 February 2016 (UTC)

Is it a fact that wine will freeze at normal freezer temperatures? If so, a simpler approach would be a kitchen timer. Like giving it 5 or 10 minutes and then the ringer will remind you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:31, 28 February 2016 (UTC)

Champagne freezes in the freezer, speaking from recent experience :) I think kitchen timer is a good suggestion, the trick will be what time to set it for, I think 10 minutes is probably too short, it would also depend considerably whether you are starting with a bottle from the fridge or from the cupboard. From the fridge you probably just want to drop a couple of degrees, from the cupboard you might need to drop ~20c. Vespine (talk) 22:55, 28 February 2016 (UTC)

Please send me several bottles of champagne and I'll get back to you on this question. General Ization ^Talk 01:39, 29 February 2016 (UTC)

Air doesn’t conduct heat as well as water. Quicker to purchase (say) the Seek Thermal app (works with Android and iPhone) then fill Ice Bucketwith 1/3 water (if you drink Champaign, surly you can afford one of those), insert magnum and fill with ice. In just 15 to 20 minutes (time this on your Android Alarm Clock app) it should register on your thermal infrared camera as being the proper temperature (8˚-9˚C/46˚-48˚F). For Aluminium Beverage Cans remember to reduce the time and generously dilute contents with lots of vodka -which should also share the ice bucket. Also, if you boil (ideally) either deionized water or distilled water or as a last resort tap-water (to expel dissolved gases) and make your ice from that. The ice will appear more clear and crystalline (from the Greek meaning ice). For Cola, one can miss this stage out unless the vicar is coming to tea. It may be a good idea to half the amount of vodka as well on these occasions but do inquire first, so as not to offend.--Aspro (talk) 23:12, 28 February 2016 (UTC)

Seek Thermal requires an app and an external device - a (roughly) 300 dollar microbolometer that attaches to your mobile phone. Here are details from the manufacturer. It's a pretty nifty device... but I'm not sure it provides any functional advantage over a thermometer for this particular use-case. Nimur (talk) 00:31, 29 February 2016 (UTC)