Wikipedia:Reference desk/Archives/Science/2016 November 15

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 15

FOD

If an F-16 makes a low-level run at treetop level and a bunch of leaves and twigs gets sucked into the engine, can it cause FOD? Or will the leaves and twigs pass harmlessly through the compressor and get burned up in the combustion chamber? (Question inspired by the Flight Simulator X mission "20th FW -- Photo Recon" from the F-16X mission pack, in which I had flown so low that my virtual fighter jet actually passed through some virtual foliage once or twice without crashing.) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:19, 15 November 2016 (UTC)

Yes it can. But it depends on the amount of solid material entering the engine. A few leaves or a few twigs might not cause the engine to stop operating but that would be good luck, not good airmanship, so good pilots are diligent in avoiding risks of that kind. Even if the pilot survived the encounter with leaves and twigs he is unlikely to survive the ensuing encounter with his Commanding Officer. Dolphin (t) 12:02, 15 November 2016 (UTC)

"First Lieutenant K--, YOU'RE FIRED!" 2601:646:8E01:7E0B:D8B3:DDFB:72C9:4D67 (talk) 12:48, 15 November 2016 (UTC)

Butterfly vs. fighter jet

Now suppose that the selfsame F-16 on the low-level attack run (see above) hits a butterfly -- and further suppose that the critter is not sucked into the engine, but instead impacts on the wing leading edge. I know that the fighter jet will be unharmed and the butterfly will be killed (that much is obvious, unless by some magical metamorphosis it becomes an Iron Butterfly), but what exactly will be the manner of the critter's demise? Will it be: (a) squished against the wing leading edge, as against a car's windshield; (b) sliced in half by the wing leading edge; (c) deflected by the airstream and then splattered on the wing surface; or (d) deflected by the airstream and then torn to bits by the boundary layer turbulence? In other words, when the jet lands back at base, will the ground crew see any trace of the critter on the airframe? (Assume that the jet is flying at 250-300 knots (and therefore shock waves are not a factor) and that both the leading-edge and trailing-edge flaps are completely retracted.) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:34, 15 November 2016 (UTC)

The mass of a butterfly is small so the force required to make the butterfly follow a curved path is also small. I predict the butterfly will be swept along the streamlines, even though they are curved, and pass around the wing. However, the violence of the maneuver, and the turbulence, are likely to seriously damage the wings of the creature so it is unlikely to survive. Dolphin (t) 12:06, 15 November 2016 (UTC)

So (d) is most likely? Thanks! 2601:646:8E01:7E0B:D8B3:DDFB:72C9:4D67 (talk) 12:44, 15 November 2016 (UTC)

We can't make reliable predictions without rigorous analysis, but yeah, I think that's the result of Dolphin's reasoning. Consider that the effective reynolds number for a butterfly in air means that momentum is basically tiny compared to viscous forces. I.e. butterflies are rather high drag, and smashing one into the leading edge of an airplane is hard, similar to how catching a dandelion pappus is hard [1]. SemanticMantis (talk) 16:27, 15 November 2016 (UTC)

Anecdotally, I've seen bugs splat on aircraft propellers and wing leading edges plenty of times. By the time I inspected the splat, I could not identify the organism by species or genus.

One of the clubs I often fly through - Blue Line, at RDU, regularly operates Diamond aircraft (cruise speed around 140 knots) through the hinterland of North Carolina. Standard operating procedure after every flight is for the pilot in command to wipe down the leading edge of the wing and remove the bug splatter. (It's a rough life flying). This policy keeps the planes looking really clean, but it's a testament to the fact that bugs splat on the leading edge.

The worst bug splatter I've ever seen was mid-summer at KWLW on approach in a Bonanza (approach speed is about 90 to 100 kts).

I don't know what happens to bugs when they encounter an F-16: it's a cleaner leading edge (in the aerodynamic sense) and is often flying much faster. I did find Siochi et al, Insect residue contamination on wing leading edge surfaces (2011), a technology report hosted by NASA's NTRS server. The report covers the topic really well, and cites lots of other sources, and it's a great example of quantitative experimental science: "Quantification of insect excrescence surface coverage was evaluated by a series of digital photographic image processing techniques." Here's more on that research group: Nothing Bugs These NASA Aeronautical Researchers.

As the Airplane Flying Handbook and the PHAK both take great pains to remind us: even nearly invisibly small disruptions to the airfoil surface can have dramatic performance impacts on the aircraft's drag and stall characteristics. PHAK 2-5: "Even though the surface appears smooth, it may be quite rough when viewed under a microscope. A thin layer of air clings to the rough surface and creates small eddies that contribute to drag."

Nimur (talk) 16:59, 15 November 2016 (UTC)

User:Nimur, of course I'm not denying the possibility of a butterfly hitting the leading edge of an airplane wing, I merely speak in terms of naive probability. I'm pretty sure my bit about effective reynolds number is apt, but I'd be curious to hear if you think otherwise. Also of course you have no record of the potentially much greater number of insects that came very close to the wing but got swept away from the craft along streamlines, leaving no residue :) SemanticMantis (talk) 17:40, 17 November 2016 (UTC)

(Non) conservation of pH

Ordinarily, we tend to assume that pH acts like a conserved quantity. Adding acid makes a solution more acid, and adding base makes it more basic. Even when compounds react, a person tends to think that a strong acid will create an acidic product. The supreme expression of this sort of belief might be the alkaline diet, in which it is supposed that certain foods create alkaline conditions throughout the body. Even if it rapidly gets into strange detail like eating citrus fruits to do this, much of it can be excused in that CO2 (i.e. carbonic acid) is excreted through the lungs to make up the difference.

On the other hand, there is the situation with borates, in which, as far as I understand, adding an alkaline borate buffer to a solution of glucose might cause that solution to become more acidic - our article says the pKa changes from 9 to 4! Much of this has to do with the interaction of hydroxyls in the borate (which absorbs an OH- from water) with vicinal diols. There is a paper with various applications here, though not all those I wonder about. Of course, more dramatic changes in pH with noncovalent associations happen in biology, but there the number of H+ affected is so small that it doesn't seem like you could change a solution's pH with it.

Q1: How much (naively) unexpected change of pH can you get by mixing glucose and borate?

Q2: Are there more dramatic overall solution pH that can be made with other small molecule associations when mixed?

Q3: It seems like you might use this to rapidly cycle the pH of a solution, perhaps even thousands or millions of times a second. For example, if flexible linkers terminated in borates were attached to a solid support covered with glucose molecules, you might apply a negative electric potential and abruptly separate them, or some other change in conditions might make the linker rigid, without actually having current flow through the solution (beyond a small capacitance). How fast could this really go? Are there existing ways to change solution pH quickly without adding anything to it? It seems like this could have some application akin to polymerase chain reaction, though honestly I have no idea what. :)

Wnt (talk) 16:18, 15 November 2016 (UTC)

pH is not a conserved quantity. There is no physical law that implies pH ought to be conserved. In fact, the easiest counter-example is to observe the behavior of any buffer solution, to which acid or alkaline can be added without meaningfully altering the pH.

Review pH; stoichiometry; conservation law; dynamic equilibrium, as it applies to chemistry.

Furthermore, because pH is measured on a logarithmic scale, there's no good reason to believe that any "empirical" conservation law you concoct would fit well to the data of any specific experiment.

It is worth reviewing the definition of acid, base, and reviewing the complexities of these definitions. pH is only one among many ways that we quantify acidity or alkalinity. There exist many complex chemistries in which the simple definitions, like the concentration of ionized hydrogen that is measured using pH, become problematic.

I'm sure we can proceed to answer your questions (Q1 through Q3), but we need to start at the baseline by dispelling any incorrect notion about pH: it is not a conserved quantity.

Nimur (talk) 16:39, 15 November 2016 (UTC)

I think the OP may be confusing things related to the autoionization of water and the implications for acid-base equilibrium. It is true that, for any PURE substance added to water (at standard conditions), pH + pOH = 14 always, which means that raising the pH means a subsequent drop in pOH and visa-versa. However, this stops being true when we have complex equilibria due to the common ion effect and other issues. Once you have "acid + water + something else", the "something else" makes the situation much more complex. --Jayron32 17:16, 15 November 2016 (UTC)

I understand that pH is not really conserved. But adding acid or base to a buffer does change the pH, and in the appropriate direction, and by a quantity that is roughly commensurate with the molar quantity of weak acid/base present already, so it isn't really that good of a counterexample.

I should add that with some further searching I found this paper in which acid-base cycling is done with adsorbed hydrogen ions on silver, with change of 4-5 pH units. Meanwhile, I was daydreaming about changing pH entirely in solution... I wonder if it is possible to identify an IR frequency that will specifically disassociate the borate-glucose complexes, so that pulsing laser light at the solution could repeatedly alter its pH, and without the limitation of proximity to a solid support. Wnt (talk) 21:21, 15 November 2016 (UTC)

Plant-based diet and healthfulness

I've been watching all these food documentaries lately. However, looking at the diets of vegans, vegans use nutritional yeast to avoid nutritional deficiencies. Yeast is a type of fungi, and fungi are more animal-like than plant-like biologically. Mushrooms are also part of the fungi category, but vegans claim that they can it because they are "not animals". Scientifically, they are not classified as animals, but they aren't classified as plants either. Because fungi are more closely related to animals than plants, shouldn't they be considered "meats" and vegans are really "meat-eaters"? In the food documentaries, there seems to be only two options - plants (in the form of colorful fruits and vegetables) or animals (in the form of really big livestock). In reality, people can eat arthropods and mollusks and other invertebrates. The animals that people mostly eat in developed countries are vertebrates (members of the chordata phylum). The domesticated animals are eaten by humans, who are supposed to be limited by the supply of animals. But humans don't want to limit their own population. They want to grow and breed exponentially, because somehow death is often associated with sadness and grief and must be stopped even though it's part of the circle of life. So, eating megafauna becomes unsustainable. Is there any health-related research in eating sustainable forms of meat, like bugs? What about the ethics of eating bugs? Based on the sentience argument, are bugs able to feel pain, and if they can't, can they be eaten? 66.213.29.17 (talk) 17:16, 15 November 2016 (UTC)

Relating to your last points, see Entomophagy [2] [3] [4] [5] [6] [7], although these are mostly about the economics and environmental issues rather than health or pure ethics. Nil Einne (talk) 17:25, 15 November 2016 (UTC)

The FAO has a great document on entomophagy, including bits on how it can help worldwide food and feed security, as well as some health info [8]. SemanticMantis (talk) 19:07, 15 November 2016 (UTC)

Of course, Western cultures have no problem eating close relatives of insects, the decapods. Don't underestimate the power of cultural relevance to dietary concerns, though. While many cultures eat insects regularly as a staple food, demanding that cultures that don't eat something (for whatever reason) start eating them is not so simple. It isn't just convincing westerners that biologically, shrimp and locusts are closer relatives than you are to either, convincing westerners to eat said locusts involves more than just knowing that. There are numerous examples where cultural insensitivity to dietary concerns caused major issues, i.e. the Sepoy Revolt of 1857... --Jayron32 19:47, 15 November 2016 (UTC)

Even more recently, the 2013 horse meat scandal was a huge scandal in the UK and other parts of Europe; foods advertised as containing beef were found to contain horse meat – as much as 100% of the meat content in some cases. Massive amount of fuss here in the UK. DrChrissy ^(talk) 20:11, 15 November 2016 (UTC)

The horse-meat scandal wasn't just about squeamishness about eating horse. If meat being sold as beef is actually horse, then it means someone somewhere along the supply chain has been lying about what they are selling, which in turn means you can't be sure of the provenance or safety of the meat. Is it luxury-grade horse meat that ended up in cheap ready-meals by mistake? Or is it from a diseased, drugged-up old nag unfit for human consumption, that was destined for the glue factory until some con-artist realized they could make more money by passing it off as beef? Iapetus (talk) 10:29, 16 November 2016 (UTC)

I'm not sure I follow your line of argument about fungi being classified as meats. Considering I'm not even sure many people will call any part of an insect meat, the evolutionary relationship doesn't seem that relevant. Fungi are distant enough from all animals that they are not considered animals under nearly all classifications. They obviously aren't plants either despite the occasional historic classification together, so it's probably fair to dispute someone who claims they only eat plants but who regularly consumes fungi. If you didn't want to say something it would be simplest to say the person eats fungi and plants rather than call them a meat eater because they consume something almost no one considered meat and for which there isn't even a good scientific argument. Nil Einne (talk) 17:34, 15 November 2016 (UTC)

If this devolves purely into a matter of definition of words, then we need to make clear up front: scientists often define many words differently than the definition that is used in other contexts. These definitions are not always universally agreed upon. Sometimes, differing definitions of the same word, as used by different communities, are mutually exclusive. The most prolific example might be the use of the word "fruit" in the sense of cuisine, and the use of the word "fruit" in the sense of plant biology.

The first step to approaching these questions with scientific rigor is to agree on our definitions, so - before we dive deeply into the question, let's start with some ground rules: who defines the terms that we are going to discuss? Even the word "vegan" is applied to a fairly wide variety of differing preferences and dietary restrictions - although some people may cling to a specific and strict definition, it is easy to find others who disagree. Furthermore, we can't usefully discuss motivation for any specific food choice when that choice is made by a large and diverse group of people. So, if we are holding ourselves to the standard sort of rigor and clarity that we expect from a scientific statement, we can not accurately state that "all vegans" exercise any specific food choice - and so debating the minutia about that choice is futile.

Nimur (talk) 17:47, 15 November 2016 (UTC)

Veganism is one of those things which suffers dearly from the No true Scotsman fallacy. --Jayron32 17:52, 15 November 2016 (UTC)

We have an article Pain in invertebrates. DrChrissy ^(talk) 17:56, 15 November 2016 (UTC)

But the key part of the OP's question doesn't seem to be about definition of veganism though, instead whether it makes sense to call fungi meat. As I mention, neither the lay person definition, nor the scientific definition (in so much as there is one) is likely to include any part of fungi as meat. So it makes little sense to say someone is a meat-eater because they eat fungi. Whether they are vegans or not is, IMO besides the point of what the OP said. You could say the issue of definitions arises in whether to call fungi, plants but IMO it's still far from simple. Even under the layperson definition, fungi are often not considered plants. (They may be called vegetables.) P.S. You do get the complicating factor meat substitutes. Mostly vegans, vegetarians and meat eaters agree these are not meat. However modern science may blur the lines. Cultured meat as mentioned below may be one example. However there is also stuff like that Impossible Foods burger that got a lot of media attentions a few months back [9]. But I'm not sure there's any reason these just relate to fungi. I believe yeast culture was used to produce the heme for the impossible foods burger, but in other situations the use of bacterial or plant culture could arise. And culture meat is an example where you have animals cells, but really something either science o the lay person would necessarily call an animal and in any case fungi just does edit: not arise here edit: so this is unrelated to whether to call someone who eats fungi a meat-eater. Nil Einne (talk) 09:06, 16 November 2016 (UTC)

BTW I hinted at this in my earlier posts, but will make it clearer now. It seems to me if you're making a big deal over eating meat you're missing the point. Especially when it comes to veganism. Whatever people may agree or disagree with definitions, most of them talk about animal products not meat. After all, few people are going to call milk or eggs, meat. Or for that matter feathers, fur, bones etc. But these are generally rejected by veganism. [10] Even if we talk about vegetarians and others who are less strict, it isn't uncommon they will reject animal products which no one calls meat. Some may say they don't eat meat (but potentially not only meat) especially when offered meat, but actually the meat-eating thing seems more likely to be something someone who isn't vegetarian/vegan will say e.g. they really like meat so can't bring themselves to adopt a vegetarian or vegan diet. In other words, getting back to the point I made in my first comment, it's pointless and actually a little silly to try and argue that people who eat fungi eat meat. You're adapting a definition almost no one (whether scientific or layperson) uses and missing the point of veganism and vegetarian arguments. To be clear, I'm not saying there's anything wrong with discussions of what veganism and vegetaranism mean, the ethics and logics of such practices (including whether it makes sense to include item X e.g. basically anything in kingdom animalia no matter whether it's a waste product of the industry or harm suffered in collecting it but nothing that is fungal or plant derived), etc etc. But simply such discussions should be based on those considerations instead of whether people eating fungi are "meat-eaters" because you're adopting some very weird definition of meat. Nil Einne (talk) 02:35, 17 November 2016 (UTC)

See also cultured meat. Count Iblis (talk) 20:03, 15 November 2016 (UTC)

Mushrooms are not really a meat substitute [11] (though they provide a pleasant umami flavor and have their own nutritional benefits, they are not nearly so protein-rich). There are of course some interesting phylogenetic outliers that those wishing to avoid vertebrates could explore - molluscs, obviously, are a pleasure, though calimari is not particularly unintelligent, and in Japan they do the oddest things with jellyfish, sea cucumbers, sea urchin gonads [12]; also I've read brittle stars, which seems difficult but seems like an intriguing idea as they take over from everything else that's been fished out of the ocean. Wnt (talk) 21:40, 15 November 2016 (UTC)

Or one can follow Patrik Baboumian's advice and eat the right combination of protein from plant sources. Count Iblis (talk) 01:11, 16 November 2016 (UTC)

What makes meat meat? In part, it is having the properties of meat, which include collagen, the (literal) glue that holds a person or animal together, and perhaps hemoglobin, which makes for proper raw and bloody meat. Well, collagen is widely dispersed throughout all known animals [13], and is considered in that source to have arisen with them; but there is a 1996 paper which, based on less than a complete gene sequence, makes an argument that fungal fimbriae are made of collagen [14] There is certainly room for a No True Scotsman argument here, but one which leaves us with a more finely honed definition of meat at the end. Hemoglobin is also very widely distributed, yet excludes some invertebrates e.g. where hemocyanin predominates.

Now lab-grown meat is doubtless meat, that I can't argue with, yet it is a mystery meat that we will never eat, and which will linger on only due to idealistic donations by those with a meatless agenda. Some of the problems with it are: (a) literally the only hormones in it are added hormones, so people who would turn up their noses at animals injected with a few extra growth hormones would be in the seventh house of freakout at the sight of it, (b) tissue culture is either incredibly prone to infection or else is done in the presence of multiple antibiotics, more stuff people don't want in their food, and worst of all (c) cultured meat lacks the liver and kidneys to clear out its wastes, so it relies on an incredibly inefficient process of putting on special growth media only to throw it away while most of the nutrients are untouched because of the accumulating waste, and ending up with meat that tastes like liver anyway, but also (d) current culture methods tend to lean on fetal bovine serum or similar products that are not even vegan... this is never going to happen, it's just smoke and mirrors. We could come up with some high-protein algal or bacterial product (note though that Soylent was recalled, not for the reason you'd think), or even synthesize protein from scratch chemically (Yummmm), but meat in a petri dish doesn't make any sense. If you want 'ethical' meat just invent a strain of acephalic cattle. Wnt (talk) 23:58, 16 November 2016 (UTC)

Meat is actually easier to define than that. Meat is defined as animal flesh. Flesh is "muscle and fat". If it doesn't have muscle, it isn't meat. Fungi don't have muscle, ergo, they don't have meat. Incidentally, the non-meat parts of animals are called offal when eaten. --Jayron32 02:33, 17 November 2016 (UTC)

The Rising of the Moon

At a given location, on average, how much later does the Moon rise on one evening compared to the previous evening? -- Jack of Oz ^{[pleasantries]} 20:35, 15 November 2016 (UTC)

It might depend on your exact latitude, but here is a utility that will allow you to enter your location and find the moonrise and moonset times for any day of the year for anywhere on earth. --Jayron32 20:37, 15 November 2016 (UTC)

That's a start, but I'll need more. For the 2 weeks starting on 11 November at my location, the sequence of gaps is (hours and minutes):

• 1:10, 1:12, 1:12, 1:12, 1:09, 1:03, 0:56, 0:48, 0:42, 0:38, 0:27, 0:31, 0:31.

So for this fortnight it seems to vary between extremes of 27 minutes and 1 hour 12 minutes. I have no idea whether this cycle is representative of the whole year. -- Jack of Oz ^{[pleasantries]} 21:05, 15 November 2016 (UTC)

Very simple. The Moon passes the Sun every 29.53059 days (variation: 29.2-29.9). So the number you're looking for is 24/29.53059 hours or 48.763 minutes. The Moon rises only once a tropical month at the poles, so this would not work at latitudes where the Moon sometimes doesn't rise for days at a time. Sagittarian Milky Way (talk) 22:30, 15 November 2016 (UTC)

Thanks. I think that works as a world-wide average, without regard to latitude. My latitude-specific search (below) gives a slightly larger average of 50.3 minutes. -- Jack of Oz ^{[pleasantries]} 22:53, 15 November 2016 (UTC)

Actually I made a mistake, JackofOz. There are 24/29.53059 hours moonset latening per day (long term average) but only for 24 hour days. The c. 50 minutes per day mojo is actually working on the moon for a few percent more than 24 hours per moonrise so the answer is 24/28.53059 hours (because between New Moon and New Moon the eastern horizon laps the Sun 29.5 times but laps the Moon only 28.5 since the Moon had lapped the Sun once (during it's monthly cycle of phases)). Leap seconds keep the clock in sync with the mean Sun so over very, very, very long averaging times (much longer than a fortnight) it should approach 1/(synodic month-1) (in units of regular days) — 50.472 minutes in the modern era. Sagittarian Milky Way (talk) 01:01, 20 November 2016 (UTC)

Thanks. Even closer to 50.3 minutes. Good. -- Jack of Oz ^{[pleasantries]} 01:38, 20 November 2016 (UTC)

This page will generate a table for your location for an entire year. Use Part B for worldwide locations, and the pulldown menu lets you switch to moonrise and moonset times. --Jayron32 21:09, 15 November 2016 (UTC)

Thanks. After a few manipulations, I see there's a regular cycle that repeats 13 times a year; never less than 30 minutes, never more than 1 hour 13 minutes. (It's not odd that the first site Jayron provided above gives a lowest gap of 27 minutes rather than 30, since I used rough rather than exact coordinates for that search). The average for this location is 50.3 minutes. That's good enough for my purposes. -- Jack of Oz ^{[pleasantries]} 22:50, 15 November 2016 (UTC)

Resolved