Wikipedia:Reference desk/Archives/Science/2015 November 9

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November 9

Asymmetrical airplane seating.

Several smaller airplane types have asymmetrical seating arrangements such as AB_CDE or A_BC (where "_" represents the aisle). Although the asymmetry is near the plane's centre line it must cause some imbalance. Is this compensated for by ballast or the arrangement of other components, or by aerodynamic trim settings, or by the pilot's control, or is it negligible ? 99.224.93.200 (talk) 02:04, 9 November 2015 (UTC)

Yes, it's compensated for. A commercial aircraft's crew (including the ground crew that loads cargo) has to take into account the load distribution of the craft. The pilots have to compute the laden weight of the craft before takeoff, because they need it to calculate things like the V speeds, as well as how much fuel to carry. If necessary they'll sometimes ask passengers to move around to even out the weight distribution; this is more common on aircraft that are smaller or have many empty seats. --71.119.131.184 (talk) 02:42, 9 November 2015 (UTC)

I think that's only the fore/aft loading and center of gravity. Port/starboard loading is rarely considered. Note that many aircraft can have unbalanced fuel loads in each wing which have a much larger moment than any centerline aisle gap. --DHeyward (talk) 03:18, 9 November 2015 (UTC)

Hmm, I'm not disputing what you're saying, but I know some planes have fuel lines that can transfer fuel between the tanks. Is that more for ensuring one side doesn't run out of fuel? --71.119.131.184 (talk) 03:39, 9 November 2015 (UTC)

The fuel can get out balance and gravity is the biggest culprit, but left/right imbalances don't normally disturb stability. One of the differences in a commercial jet and and private small planes is the relative differences between the center of lift and center of gravity. In commercial jets, the aircraft is loaded mor ecarefully with less stability to improve fuel efficiency. It's all about keeping the center of gravity and center of lift in their proper places. Fuel transfer that's done for efficiency would be to move fuel from a forward position to an aft position. Left/right imbalances just aren't as important for stability. Airplanes turn by creating left/right lift differences which rarely cause a problem. But pitch up problems create stalls and an unrecoverable pitch down will just crash. A plane can do a 30 degree banking turn without losing altitude until it runs out of fuel but a 30 degree pitch up climb will eventually stall. --DHeyward (talk) 08:52, 9 November 2015 (UTC)

Some aircraft can sustain a 30° pitch attitude for an indefinite period of time... but no civil pilot may execute that maneuver in the United States "unless each occupant of the aircraft is wearing an approved parachute." (14 C.F.R. §91.307(c)(2)). Thirty degrees of pitch is a pretty steep climb or dive!

An aerodynamic stall is caused when the angle of attack falls too low, and the flow of air over the wing becomes turbulent. As long as the aircraft can maintain a high airspeed, it may be able to sustain a steep climb without stalling. Some airplanes can do so because they have powerful engines - rather, a high power-to-weight ratio, so they have enough thrust to keep going fast while pitching up. Some aircraft can enter a pitch-up at high speed and maintain airspeed for a while using their inertia. However, each aircraft and each pilot needs to carefully consider their aircraft's weight and balance, as well as its operating limitations. Steep climbs, especially if abruptly executed, can load an aircraft beyond its safe limits, even at high airspeeds or with full thrust produced by a powerful engine. A classic failure-mode is the "high-G stall" in which a confused pilot stalls at very high airspeed due to an overly-abrupt pitch-up.

The canonical reference for this question is the Aircraft Weight and Balance Handbook, a free textbook from FAA that explains how aviators can determine if their airplane is safely loaded and balanced. The very same rules of law and science apply to commercial and air transport aviators.

Nimur (talk) 17:11, 9 November 2015 (UTC)

This is true but concern is center of lift and center of gravity. Left/right is not an issue so high angle rate of turns don't run out of balance the way a climb or descent will. Weight and balance is generally always an issue of a change of the relative position of the center of lift with respect to the center of gravity along the longitudinal access. Even fuel in a swept wing is about the weight/CG being aft or fore of the center of lift. It's very rare that left/right weight changes compromise flight stability. --DHeyward (talk) 07:21, 10 November 2015 (UTC)

That's because, as DHeyward has correctly noted, most airplanes are designed with excellent margins for stability on the roll axis. I seem to recall reading about one airplane that did not have such great stability on the roll axis when a different question came up a few weeks ago - why doesn't the B-2 Spirit need a rudder...? That aircraft is unusually shaped - and its payload is unusually configured, with very dense and massive cargo that can be released during flight - which adds yet another dimension to the complex problems of aerodynamic control on that platform.

Civilian airplanes designed for passenger air transport are categorically designed for very good stability in all axes. Moving the mass of passengers around a little bit probably has a small impact on the stability margin, and probably barely even registers to the pilots when they adjust their roll trim. In very small aircraft, there is no roll trim: pilots just have to hold the plane steady using skill! Nimur (talk) 17:33, 10 November 2015 (UTC)

What would happen if the only other guy in the plane went from the front seat to the stern and the pilot didn't adjust and they're in the worst kind of plane to do that in? What plane is that? Sagittarian Milky Way (talk) 21:55, 10 November 2015 (UTC)

Cancer in inverterbrates

Here is one of the strangest news stories I have read in a long time. http://www.foxnews.com/health/2015/11/05/man-dies-after-tapeworm-inside-him-gets-cancer.html?intcmp=ob_article_footer_text&intcmp=obnetwork

As Veterinary oncology says, there has been a lot of research into cancer in cats and dogs, and presumably also into farm animals. But what “lower” animals that are still multi-cellular and therefore metazoa (that is, higher animals) get cancer? We know that elephants seldom get cancer because they have multiple copies of an anti-tumor gene that is present in all mammals. Elephants have been long-lived longer than humans have. We now know (whether we knew it before) that flatworms can get cancer. We now know that, in rare cases, it can actually kill a human.

The whole article on cancer seems to be about cancer in humans, and it should be mostly about cancer in humans. I had known that there had been research into cancer in sharks, and that there is argument over whether sharks get cancer.

We now know, whether we did or did not, that worms can get cancer. This does imply that cancer appears very close to the base of the evolutionary tree. (Don’t get your backbone removed. It won’t help.) What is known about cancer in inverterbrates? Maybe we need an article, or a section of an article. We now know that flatworms can get cancer, and so anything above them on the tree presumably can.

Comments?

Robert McClenon (talk) 03:29, 9 November 2015 (UTC)

This isn't really the place to just have a discussion. Do you have a specific question other than, what do people think? I've found a few research articles just by googling inverterbrate cancer. I also remember reading that there is good evidence dinosaurs had cancer, (for those people who claim it's a "modern disease". Vespine (talk) 03:55, 9 November 2015 (UTC)

I don't see any reason why all multi-cellular animals and plants wouldn't be subject to cancer. Indeed, if we find any which appears to be 100% immune, we might do well to study it. StuRat (talk) 05:57, 9 November 2015 (UTC)

My question was prompted by the fact that Wikipedia doesn't answer what I thought was a reasonable question, whether invertebrates and plants get cancer. In this one very strange case, a human died of flatworm cancer. (He might have died from the flatworm anyway.) I asked the question because Wikipedia doesn't answer it. Robert McClenon (talk) 08:24, 9 November 2015 (UTC)

Devil facial tumour disease is an interesting animal cancer. StuRat (talk) 08:41, 9 November 2015 (UTC)

Hence Category:Types of animal cancers.--Shantavira|^{feed me} 08:53, 9 November 2015 (UTC)

There is a species which is apparently immune, and there are studies into it - see Naked mole-rat#resistance to cancer. Now, the fact that this is a surprising discovery would suggest than cancer is prevalent in most other well-studied species. MChesterMC (talk) 09:30, 9 November 2015 (UTC)

That link is case sensitive: Naked mole-rat#Resistance to cancer. StuRat (talk) 17:12, 9 November 2015 (UTC)

• Before anyone says otherwise, sharks do get cancer. When plants get cancer, that's usually called a gall (although not all galls are equivalent to animal cancer) – see crown gall for an example. Smurrayinchester 09:39, 9 November 2015 (UTC)

I'm not sure it's reasonable to equate any plant galls with "cancer", much less all of them. Our article says they're analogous to "benign tumors or warts". While I'm sure there are subtleties this doesn't cover, the usual sound-bite definition of "cancer" requires the potential for metastasis, and I don't see any allusion to that possibility in the gall article. --Trovatore (talk) 02:21, 10 November 2015 (UTC)

Cancer has been well studied in Drosophila, and there are many proto-oncogenes involved that are homologous to those in humans. [1] Therefore, cancer traces back to the Urbilaterian, at least. However, I didn't quickly find information about whether Cnidaria are subject to it... I really ought to look harder. Wnt (talk) 13:32, 9 November 2015 (UTC)

Peto's paradox is probably the interesting one here. All large animals have protection against cancer but iut just isn't that important for small short lived animals. Dmcq (talk) 17:09, 9 November 2015 (UTC)

Survival: Humans Unable to Eat Leaves for Nutrition. The Whys and Hows. ?

So many herbivores eat leaves, but it has always been said that humans can't eat leaves (with a few exceptions), supposedly because they are so full of cellulose and so fibrous, and evolution has seen us become lacking of the necessary enzymes to break cellulose down. Maybe this is so, but when I learn or read about people in survival-situations, lacking food, it seems so... unnecessary to starve when there's trees and leaves everywhere, because there is nutrition in them, albeit not that much.

I mean, wouldn't it be better to eat at least a little bit leaves than nothing?? Leaves are not that nutritious, I know, which is why many herbivores spend big chunks out of a day simply eating, but so long as we ate only a little bit and not too much at the time, shouldn't our bodies be able to cope with it better than having no calories at all? What if one boiled the leaves first, would it make any difference at all?

I've been told that Pine-needles is one of the exceptions, that this is in fact useful as "survival-food". Is this true? Pine-trees are widespread in abundance. It would have made things easier, but surely it ain't that easy, no?

2A02:FE0:C711:5C41:5D0C:5C73:C6D4:4C90 (talk) 10:19, 9 November 2015 (UTC)

Few animals can actually digest cellulose themselves. Most animals that eat cellulosic material rely on microbes in their gut to do the actual digesting. Their bodies then absorb the breakdown products. So, "become lacking of the necessary enzymes" is not the case; our ancestors never had the enzymes to begin with. The evolution of herbivory is a good object lesson in evolution. The key thing to remember is that developing and maintaining a trait incurs a cost to the organism. Traits only become widespread in the presence of favorable selective pressure. Herbivory is an expensive trait, as it promotes heavy specialization; a digestive tract optimized for digesting cellulosic material is not very good at digesting anything else. So, species generally won't develop herbivory unless their available food sources are constrained. The other key point about evolution is that it's not intelligently directed. Evolution is the "blind watchmaker", as Richard Dawkins put it. Evolution can only act on existing organisms, groping blindly for solutions that promote fitness. So we get ridiculous jury-rigged solutions like pandas, who try to digest bamboo with a carnivore's digestive tract, or herbivores who have to eat their own feces in order to digest anything. Even if there are situations where an organism might benefit from herbivory, natural selection can't just pull the trait out of thin air. One other thing of note: you should remember that plants don't want to be eaten (except, in the case of flowering plants, their fruits, and even then only by the right species and at the right time). Many plants deploy defenses against things trying to eat them, which is something else herbivores have to adapt to. --71.119.131.184 (talk) 11:03, 9 November 2015 (UTC)

There are plenty of leaves humans can and do eat. Here is a very long list of leaves humans regularly eat (I had some Senegalia pennata with dinner tonight myself).--William Thweatt ^TalkContribs 11:14, 9 November 2015 (UTC)

We don't get much energy from eating leaves. If we kept eating leaves we wouldn't have become intelligent beings. We relied on other animals to digest leaves. We killed that animals and cooked their meat and got much more energy efficiently. We spent less energy and got more energy. So we have lot of excess energy in body. We spent that excess energy in building intelligence. - Supdiop (T🔹C) 11:45, 9 November 2015 (UTC)

Agreed that leaves don't have much energy in them, but other plant parts do. Look for where the plant stores it's own energy, either for the next generation (seeds, nuts, berries, fruit) or for itself (root vegetables, tubers). StuRat (talk) 18:46, 10 November 2015 (UTC)

FYI, seeds store energy for the offspring, but fruits store energy to attract dispersers], e.g. frugivory. SemanticMantis (talk) 20:16, 10 November 2015 (UTC)

The extraordinary kinetic stability of cellulose never ceases to amaze me. We know the potential energy is in there - just toss a log on the fire! But as described at [2], cellulose is chemically almost the same thing as starch, which is so easy to degrade that you have an enzyme in your saliva that starts making it taste sweet the moment it touches your tongue. Yet - somehow, that I don't really understand - it manages to crystallize into such a configuration of hydrogen bonds that water cannot penetrate it, and for some reason that I also don't understand, enzymes can't readily cut it except at the ends. And when I say "enzyme", I mean "billions of years of evolution have failed to crack this, other than with some substandard solutions for cellulase that use such brute force that they release methane trying to get sugar subunits apart (think about that!) and more to the point require large fermentation spaces and times to get the cellulose digested. [NOTE: the below shows that I'm wrong about the enzymes not being good, and whatever I thought about methane seems wrong] Now that is tough enough, but plants are savvy to the whole notion of getting eaten and add lignins to lock it up even tighter. Lignin is somewhat similar to melanin or humic acid, or even the synthetic polymer Bakelite, which links phenols together. Wnt (talk) 13:22, 9 November 2015 (UTC)

It's a question of "quantity rather than quality" here. For humans to digest any carbohydrate, it first needs to be in the form of a monosaccharide. In order to get it there, polysaccharides need to be broken down into monosaccharides, a process that (as you note) can really only be done from the ends of the polysaccharide chain. The difference between starch and cellulose is, as you not, merely one of the length of the chain; starch is "chains short enough for humans to be able to digest reasonably completely", with cellulose being "chains too long for humans to break down before it leaves the part of their digestive system where this can happen". For example, this chart I got out of a recent scholarly article, it discusses chain length of two common starches, potato and maize, and shows that the mean chain length (number of saccharide monomer units) to be roughly 20-21 units long. As you can see here, the average chain length of cellulose polymers is somewhere over 10,000 units. Given that you can only digest these from the ends, that means that starches should (with all other things being equal) break down in the gut roughly 10,000/20 = 500 times faster than cellulose. So, given that [transit time in the digestive system varies from 24-72], if it takes 24 hours to digest and pass starches from eating to exceretion, it would take a year and a half to digest the same mass of cellulose. As in, it's not going to happen. --Jayron32 13:34, 9 November 2015 (UTC)

@Jayron32: It's not going to happen with cellulose, because AFAIK the available cellulases only work at the ends. However, amylases can have multiple activities - one exo, one endo. So a gene like human AMY1A can chop starches up into pieces - and because its rate is constant per residue and not per molecule, the starting size of the starch is going to be virtually irrelevant. (The branches are a different complication) If I remember right, I think the salivary amylase actually is just an exo activity, because it's only really "meant" to give you a taste. Wnt (talk) 15:14, 9 November 2015 (UTC)

Well, the other problem with celluloses is the degree of branching and cross-linking. In order for the amylase enzymes to get to the chain to break it apart with the "endo" mechanism would actually require a relatively unbranched chain with minimal cross-chain linkages. With 10,000-unit length polymers, there's ample entropy necessary for repeated cross-links and tangles. Interestingly, this article about the "spontaneous knotting of an agitated string" is directly relevant: the amount of "tangling" a "string" experiences is a function of its length. Longer strings have more opportunities for tangling, and cellulose "strings" are very long indeed. The amount of "tangling" simply prevents the endo-mechanism based amylases from getting in there and doing their jobs. The very short starch strings have less opportunity for tangling. --Jayron32 16:12, 9 November 2015 (UTC)

@Jayron32: I don't think so. From our article: "Cellulose is a straight chain polymer: unlike starch, no coiling or branching occurs". Think of a hemp string: there's no "give" when you pull it taut, because at the molecular level it is just straight fibers. I just looked up a hit for cellulose lignin interaction [3] that says it is electrostatic interaction with the hydroxyl groups (related to that incredible crystalline structure, I suppose?) There is also the matter of hemicellulose in the interaction - it has some contributory effect, though it is far more vulnerable to digestion. Wnt (talk) 20:06, 9 November 2015 (UTC)

Plenty of responses, I can see. Some of the information shared is pretty high-flying and it seems that some of you are very knowledgeable. Thanks for all replies. 2A02:FE0:C711:5C41:5D0C:5C73:C6D4:4C90 (talk) 15:57, 9 November 2015 (UTC)

Getting back to the original question, is it plausible that a human being in a survival situation could derive any meaningful benefit by eating leaves, say maple tree leaves or or pine needles, and nothing else? Would there be harmful effects compared to eating nothing at all? Edgeweyes (talk) 16:13, 9 November 2015 (UTC)

Lots of campers and survivalists drink pine needle tea, it has vitamin C [4]. SemanticMantis (talk) 18:11, 9 November 2015 (UTC)

Lots of other edible leaves of wild plants here [5], [6]. Really, I think people above are being a bit finnicky. Humans eat lots of leaves. They tend to not have lots of calories per mass, but they do have calories, and eating plants whilst lost in the woods (assuming you know what you're doing) is indeed a good way to survive longer. In addition to calories, you can also get vitamins and other nutrients. Oxalis, lamb's quarters, and wood sorrel come to mind as plants that are common in most of the USA that I eat when foraging in the wild that also have some useful vitamins. So while it is true that it's tough to digest cellulose, that doesn't mean that we can't get nutrition out of leaf or stalk of a plant. Roots, tubers, bulbs, seeds and fruit tend to have larger amounts of readily available nutrition, but stems and leaves are food too. SemanticMantis (talk) 18:17, 9 November 2015 (UTC)

According to The Zen Monastic Experience: Buddhist Practice in Contemporary Korea, monks there sometimes embark on a sort of fast which includes powdered pine needles amongst other wild foods. According to Biomarkers in Toxicology (p. 576), eating Ponderosa pine needles causes abortion in cattle. A number of survival blogs and forums confirm that pine needles are indeed edible, but "Pine needles have virtually no calorific value. I would not recommend pine needles as an energy source..." [7] Here in the UK, the leaves of common lime and hawthorn are tender enough to be eaten in the spring, but any later in the year, you just end up with a mouthful of inedible fibres. Alansplodge (talk) 18:36, 9 November 2015 (UTC)

I've been doing my own research today also, meanwhile waiting for replies on here, and I've learned some really interesting and cool things (from you and on my own) - most of all about Pine trees, and I am amazed at how many uses these trees can have and how much of it is edible; Pine needles, Pine cone Seeds, Cambia/Cambium (which is a "secondary tissue" just underneath the bark) and even pollen dust from some of the trees can all be eaten for nutrition. Some of it containing Carbohydrates and some of it containing *huge* amounts of Vitamin C, which several of you guys have already mentioned, more than any citrus fruit in fact, according to claims. I've also learned that grass can be chewed (but not swallowed) to obtain some small amounts of its calories by way of your saliva. Krikkert7 (talk) 19:02, 9 November 2015 (UTC)

Meh. It seems if a plant is energy rich enough to be a food source, humans have evolved an intellignce great enough to catch and eat the animals that put in the legwork. A cow can spend a lot of time turning grass into steak and humans are smart enough to take advantage of this system. Butchering is easier than grazing. --DHeyward (talk) 07:31, 10 November 2015 (UTC)

I read a science fiction story a few years ago (don't remember the author) which relates to this. In it, aliens land on Earth and find the planet with humans extinct. In every town, a monument had been built to one individual, and later defaced. The statue individual had been a scientist who discovered some dietary supplement or genetic modification which made humans able to digest grass, leaves, and other raw plant fiber the same as a herbivore. At first it was wonderful, since the starving people in various countries could now just eat the jungle/weeds/lawns/grass as if they were deer. The population levels surged until they had overpopulated, killed off the plant population needed to oxygenate the air and feed to masses, and died in starvation and war. Edison (talk) 14:49, 10 November 2015 (UTC)

Percival Zhang and colleagues published in 2012 in PNAS an article supposedly telling how to convert any cellulose (corn husks, wood) into amylose, which humans could then digest: "one-pot enzymatic conversion of pretreated biomass to starch through a nonnatural synthetic enzymatic pathway composed of endoglucanase, cellobiohydrolyase, cellobiose phosphorylase, and alpha-glucan phosphorylase originating from bacterial, fungal, and plant sources." Edison (talk) 15:44, 10 November 2015 (UTC)

OMFG I missed this. [8]: "Here we demonstrate one-pot enzymatic conversion of pretreated biomass to starch through a nonnatural synthetic enzymatic pathway composed of endoglucanase, cellobiohydrolyase, cellobiose phosphorylase, and alpha-glucan phosphorylase originating from bacterial, fungal, and plant sources. A special polypeptide cap in potato alpha-glucan phosphorylase was essential to push a partially hydrolyzed intermediate of cellulose forward to the synthesis of amylose. Up to 30% of the anhydroglucose units in cellulose were converted to starch; the remaining cellulose was hydrolyzed to glucose suitable for ethanol production by yeast in the same bioreactor." Wikilinking these till I take a better look... note we have some remedial to do here! Wnt (talk) 20:19, 11 November 2015 (UTC)