Wikipedia:Reference desk/Archives/Science/2013 February 28

= February 28 =

Emotional impact of surveillance
Suppose the following three alternative scenarios: (1) A person is placed under surveillance and told beforehand that he/she is under surveillance (without being told how, where or when); (2) The same person is placed under surveillance and not told about it, but rather is left to find out about it for himself/herself (or not); (3) The same person is not placed under surveillance, but falsely told that he/she is, for the purposes of intimidation/behavior modification/etc. My question is, of these three scenarios, which one do you think will be emotionally the hardest for the person in question, and which will be the easiest? 24.23.196.85 (talk) 05:40, 28 February 2013 (UTC)


 * As it says at the top of this page, we don't answer requests for opinions, predictions or debate. --Guy Macon (talk) 06:24, 28 February 2013 (UTC)
 * That sounds like stalking and harassment to me. Dmcq (talk) 11:36, 28 February 2013 (UTC)


 * I think it's actually a meaningful question, but unfortunately ill-posed. The problem is that (3) presumes that the subject can't directly detect the surveillance, but (2) presumes that the subject can directly detect the surveillance.  So you're really mixing up two different concepts of surveillance, and that makes the question impossible to answer in any sort of definite way.  There has in fact been some research on the psychological effects of surveillance, which is discussed very briefly in our surveillance article. Looie496 (talk) 15:45, 28 February 2013 (UTC)


 * All three would likely cause resentment, unless you're being paid for it, a la the Kardashians. ←Baseball Bugs What's up, Doc? carrots→ 17:37, 28 February 2013 (UTC)


 * Thanks! So, I take it as "not enough hard info to answer". 24.23.196.85 (talk) 06:46, 1 March 2013 (UTC)

increasing white blood cell count
My brother recently discovered he has cancer of the gullet(osophagus)- he has started receiving chemotherapy which is causing his white blood cell count to reduce to an unhealthy low level.Does anyone know of natural food stuffs that increase white cells in the blood system?62.6.188.162 (talk) 06:45, 28 February 2013 (UTC)
 * The reference desk, and Wikipedia editors in general, cannot offer medical advice.--Jasper Deng (talk) 06:58, 28 February 2013 (UTC)


 * The desire that individual foods also function as medicines to specifically cure certain serious diseases goes back to prehistory. While spectacular benefits may accrue when one eats a food that supplies a specific deficient nutrient (like citrus fruits for scurvy, or cod liver oil for vitamin D rickets, or iodine for endemic goiter) I cannot think of a single food that has more than a marginal specfic benefit for a serious dysfunction of a major organ or system. This is a fantasy that underlies the transfer of billions of dollars, however, as there are an unlimited number of quacks out there willing to take the money of those wanting to buy hope. Please understand thst a healthy diet with all needed nutrients is essential to health. It is just that I cannot think of a single major organ dysfunction (like bone marrow or lymphocytes or liver or skin or parncreas) that a particular food will reverse. Best wishes to your brother. alteripse (talk) 11:29, 28 February 2013 (UTC)

Oldest extant species
What is the oldest extant species? I know the horseshoe crab has been there for 450 million years. Is there any other species which is older? --PlanetEditor (talk) 10:58, 28 February 2013 (UTC)
 * No extant species of horseshoe crab has been around that long, though xiphosurans in general have. You may want to take a look at the article Living fossil for some insight into the matter. Deor (talk) 12:01, 28 February 2013 (UTC)
 * It's difficult enough defining where one species ends and another begins when dealing with two extant species. Trying to decide when one species goes extinct and becomes another species is almost impossible, so the standard species descriptions will be highly arbitrary. --Tango (talk) 12:35, 28 February 2013 (UTC)


 * The oldest extant species is likely to be aquifex pyrophilus at around 3.5 billion years old. I wouldn't even bother examining any candidate species that could not have existed prior to the Great Oxygenation Event. The problem is that we cannot go back in a time machine, grab a sample of a. pyrophilus, and compare it with today's sample. Another problem is that a common definition of "Species" is "a group of organisms capable of interbreeding and producing fertile offspring", which makes it a bit difficult to apply to an organism that predates sexual reproduction. --Guy Macon (talk) 12:48, 28 February 2013 (UTC)


 * The basic concept of a species is a group of individuals that can mate with each other and produce viable offspring. So you could make this question more definite by asking how far back you can go and still find something that can mate with something that exists today and produce viable offspring.  The answer, I'm afraid, is that nobody knows.  It might be only a few million years; it might be hundreds of millions of years.  (This notion of a species doesn't work for single-celled organisms that reproduce asexually, let me note.  My own view is that the term "species" ought not to be used in that situation, but I'm in a minority.) Looie496 (talk) 15:37, 28 February 2013 (UTC)


 * This intuitive concept might be true for species that mate, but what about bacteria? OsmanRF34 (talk) 16:27, 28 February 2013 (UTC)


 * I addressed that in the parenthetical note at the end of my comment. Looie496 (talk) 17:20, 28 February 2013 (UTC)


 * Sorry, I jumped to a conclusion too fast (aka speed reading). But then, how do you call different types of bacteria, when they are not species? OsmanRF34 (talk) 18:43, 28 February 2013 (UTC)
 * Depending on the context, the best choices other than "species" are probably Operational_taxonomic_unit, or perhaps "strain". SemanticMantis (talk) 19:57, 28 February 2013 (UTC)
 * Some disciplines also use "phylotype". We have a whole article on the species problem; this is tough stuff. SemanticMantis (talk) 20:08, 28 February 2013 (UTC)

two questions about flight. 1) why do helicopters have 4 blades?
1. My first question is this:

In talking about the top rotor only, why do helicopters have 4 blades, instead of just 2? (i.e. in an X configuration instead of a simple / configuration). In googling, I do see quite a few that have one long pair and one relatively short pair, but there are still 4 blades in total in an X. Why do the designs always need that? 91.120.48.242 (talk) 11:56, 28 February 2013 (UTC)


 * Helicopter rotors don't always have four blades - most only have two. Compare the Bell 212 and Bell 412. (The small rotor at the tail end of the fuselage is called the tail rotor. It serves to stop the helicopter from spinning around; it doesn't contribute to the lift necessary to support the weight of the helicopter.) Dolphin  ( t ) 12:23, 28 February 2013 (UTC)


 * I am extremely confused as when we look at the TOP rotor only (which is what my quesiton is about; please ignore tail rotors), on both of your pictures I see *four* blades in an X configuration! The first one (Bell 212) shows the long pair/short pair combination I mentioned in my question, while your second picture is an X such as all the other ones I see.  Googling Helicopter, I see only exclusively 4-blade designs, with a very very occasional / (two blade) instead of X (four blade) design of the top blades.  Why is this?  What is the role of the two short blades when it is two long + two short X design?  91.120.48.242 (talk) 12:28, 28 February 2013 (UTC)
 * There is something sticking out perpendicular to the blades, but I don't think they are blades themselves. They don't look like they'll provide any significant lift. I'm not sure what their purpose is. --Tango (talk) 12:43, 28 February 2013 (UTC)


 * The gizmo sticking out pecundicular to the blades on the 212 (and also on the UH-1, which uses the same rotor system) is a flybar - the knobs on the ends are weights which act as mass dampers to reduce the vibrations in the assembly.
 * There is a great many compromises that goes into the design of the helicopter rotor systems; heavier helicopters tends to have more blade to increase the lifting area available, usually at the cost of a more complex system to maintain and balance out. More blades can also allow for shorter bars, meaning the rotor can rotate more quickly without the tips loosing lift.
 * In short; a simple 2 bladed rotor is only suited for a light helicopter - a heavy one usually have 5, 6 or even 8 blades (Mil Mi-26). Since most helicopters in every day operations tends to be mid weight ones, it's not too surpricing that four bladed rotors are most often seen. WegianWarrior (talk) 13:01, 28 February 2013 (UTC)
 * See Helicopter rotor. 38.111.64.107 (talk) 13:03, 28 February 2013 (UTC)

Helicopter rotor --Guy Macon (talk) 13:28, 28 February 2013 (UTC)


 * As stated above, the heavier the helicopter the more lift required. Simply making the blades longer would create the desired lift but you run into the following problem: as the diameter of the rotor increases the blade tip speed increases (at a given RPM). Once this ratio nears the sound barrier you start picking up problems. See here for more: http://en.wikipedia.org/wiki/Propfan#Propeller_blade_tip_speed_limit 196.214.78.114 (talk) 11:19, 4 March 2013 (UTC)

Thank you for these answers! --91.120.48.242 (talk) 15:55, 28 February 2013 (UTC)

second theoretical question about aerodynamics
my second question about flight. this is a purely theoretical question intended only to further my understanding of aerodynamics and is not intended to have any practical application, be something i publish build or offer for sale or anything like that (indeed it is practically impossible as described in the end). it's just aerodynamics question I am asking here to further my understanding.

2. as a purely theoretical question.


 * imagine a glider similar to this: http://en.wikipedia.org/wiki/Eta_Aircraft_eta

Now imagine the following changes.
 * 1)  the wings are actually attached above (not in line with) the body
 * 2)  the body can turn under the wings via the power plant - (if it did the tail would bump into the wings if the tail didn't get out of the way)
 * 3)  one wing can deforms/turns so that it is now facing the opposite wind direction to generate lift (changed from "rotate 180 degrees over its long axis", which doesn't work).
 * 4)  the angle of attack of both wings can be changed
 * 5)  the tail is, in fact, 3 layers: two flaps and a rotor inside...
 * 6)  ...these two flaps normally totally enclose the a rotor, which is hidden.
 * 7)  ... however, they can each open (change yaw) 90 degrees (to point toward the sides of the plane), exposing the rotor inside.

The question is this. Suppose the plane goes through these steps:
 * 1)  the one wing turns around 180 degrees along the long axis deforms/turns so that it is facing the opposite direction to generate lift.
 * 2)  the angle of attack of the two wings is changed
 * 3)  the rudder flips 180 degrees along the forward-aft axis of the plane to get out of the way of the (geometrical plane of the) wings
 * 4)  the rotor on the tail is exposed by unhinging the flaps to change their yaw
 * 5)  the rotor can turn to counteract the turn produced by the power plant, thereby keeping the body of the plane straight while the wings turn.

Would this be enough to turn the glider into an efficient climbing machine (like a helicopter)? Or would the characteristics that make the wings good gliders make it a terrible "helicopter" at ANY angle of attack and the design could not possibly work (theoretically, this isn't intended to be practical but just to further my understanding of aerodynamics) for this reason.

(I imagine it might be possible that this would NOT theoretically work because the glider is designed with wings that go long distances while losing very little altitude. Conversely, it would have to spin many many many times to gain very little altitude.  However, my idea is that changing the angle of attack is enough to counteract this)?

This is not intended to be practical in any way. I am simply interested in understanding aerodynamics better through this exercise in whether such a glider would be able to climb efficiently, or, if not, what the problem would be with this?

I am really only interested in the climbing efficiency / aerodynamics, not practical problems with this machine such as the obvious one that a glider could never support a helicopter engine, fuel, and so forth. For the purposes of this question, you could even assume that a long tether from ground feeds the glider compressed air to turn the engines. My question is about how efficiently it can use that power in the configuration described.

Thanks for furthering my theoretical understanding of aerodynamics. 91.120.48.242 (talk) 12:25, 28 February 2013 (UTC)


 * I'm not sure I quite get what you're asking, but you're suggesting turning one wing "upside down" and turn the two wings into a rotor? In what case:
 * -The rotational speed would have to be pretty low, otherwise the very tips of the rotorblade would be supersonic and produce more drag than lift. This coincidently would mean that the inner portion of each wing would most likely be below stalling speed and produce more drag than lift... a lose-lose situation, really.
 * -The airfoils on a glider is usually not symetrical, and might not produce much lift at any angle of attack while upside down. Best case scenario involves having the two halves of the rotor system at different angle of attack to produce the same lift, which most lilely means they will produce different drag - causing a large inbalance of forces on the rotorhead.
 * While it might be possible to design an airplane to do what you suggest, I believe it will be at best a meadicore helicopter and a poor glider. In addition the transition between one and the other function basically means your plane will lose lift on one side and go out of control... WegianWarrior (talk) 13:14, 28 February 2013 (UTC)


 * This is a good response and answers some of the the aerodynamics questions I had. In considering a 'very long' glider like this, I was also thinking of human-powered helicopters like this: http://www.youtube.com/watch?v=MkZ2bTWvRns  - I realize these are extremely light-weight, but they are also very very long and lift themselves by turning slowly.  So I thought very long blades turning relatively slowly would be an acceptable solution.  As for your specific responses:
 * >I'm not sure I quite get what you're asking, but you're suggesting turning one wing "upside down" and turn the two wings into a rotor?
 * Sorry, as you clarified this might not work. I really mean that the wing deforms or turns so that it is facing the opposite wind direction.  This might not be practical but then again I am just interested in the aerodynamics of the new system on a theoretical level.
 * >In that case:
 * >-The rotational speed would have to be pretty low, otherwise the very tips of the rotorblade would be supersonic and produce more drag than lift. This coincidently would mean that the inner portion of each wing would most likely be below stalling speed and produce more drag than lift... a lose-lose situation, really.
 * I don't really understand this point. I looked at some of the largest helicopters built, like this: http://www.aerospaceweb.org/question/helicopters/q0284.shtml -- that page says "Each rotor had a diameter of nearly 115 ft (35 m)" as compared with my example's "Wingspan: 30.90 m (101 ft 5 in)" (which could be shortened somewhat I suppose).  So your objection would seem to apply to that helicopter as well?  Did the tips of those blades really move at "supersonic" speeds?  Can you talk more about the essential difference between the "rotors" of 115ft/35m which work on the helicopter and the "rotors" of my question of 101ft/30m which you say in theory cannot?  (Of course there might be other practical issues as well but I am trying to understand the theory first.)  On the page I linked, the Mil Mi-26 seems to be quite practical (mass-produced, and used today according to the page) and also has 106 ft (32 m) diameter rotors.  It does have 8 of them, and has a maxium take-off weight of 123,455 lb (56,000 kg), suggesting that each of the eight blades support a "15431 lb / 7000 kg" share.  In theory, then, 2 such blades might support quite a bit of weight (not saying it would be double the single share of the 8-blade design).  In that configuration does your same objection apply, that the edge must be super-sonic whereas the center simply adds drag?
 * >-The airfoils on a glider is usually not symetrical, and might not produce much lift at any angle of attack while upside down. Best case scenario involves having the two halves of the rotor system at different angle of attack to produce the same lift, which most lilely means they will produce different drag - causing a large inbalance of forces on the rotorhead.
 * Sorry you have just helped correct a mental misunderstanding. Since the airfoil is NOT symmetric the correction rotation is not 180 degrees around the long axis of the wing but a turn/deformation to face the opposite air wind direction.
 * >While it might be possible to design an airplane to do what you suggest, I believe it will be at best a meadicore helicopter and a poor glider. In addition the transition between one and the other function basically means your plane will lose lift on one side and go out of control...
 * I realize that with the correction, it is rather silly of a wing suddenly changing directions mid-flight to face the opposite direction. But if it does happen, then theoretically as concerns the rest of the aerodynamics, what are the properties of the new system that make it a poor glider or poor "helicopter"?
 * Finally, Can you also talk about what you mean by "large imbalance of forces on the rotorhead" in the case that "two halves of the rotor system at different angle of attack to produce the same lift"? It's not possible to design wings that operate at the same drag for the two angles of attack, perhaps by including some physical deformation?  I am just interested on a theoretical level, not practically.  If you did design such "wings"/rotors, what would be the characteristics or properties of such a system? 91.120.48.242 (talk) 15:05, 28 February 2013 (UTC)


 * Aeroplanes usually have more or less the same profile and twist along the whole span - ie the AoA near the wingroot is close to the same as on the wingtip. A helicopter rotor usually either changes the profile or the twist along the lenght og the blade, to compensate for the different speed the blade meets the air with. Since I was assuming a rigid wing structure, this basically means that a wing suited for a glider is unsuited for a helicopter blade and vice versa (due to the issues mentioned with either stalling on the inner blade or losing lift due to going supersonic near the tip). If we're assuming a wing that can dynaicly change it's profile as radically as you postulate.... well, if you could make that work in Real Life you would be quite rich quite fast, since such a wing would have a large number of lucrative uses - particularry in the defence industry.
 * So, postulating a wing that can radically change the profile and twist - and ignoring the loss of controll while shifting from one mode of flight to the other - then yes; a craft can be made to change between glider and helicopter.
 * Postulating a rigid wing, as I did, you'll end up with a wing that is either suited to be a glider wing or a helicopter blade - or, if you compromise, not very suited for either.
 * In regards to the very large rotors on some heavy helicopters: they work because they are designed from the outset to be very large rotors. This can be done either by giving the tip a suitable profile for supersonic flight - wich would result in a very noisy machine - or by giving the section near the root a higher AoA and/or a suitable profile for low speed.


 * In regards to the comment on inbalanced rotor heads I would assume it would be fairly self evident; if you have a rotor system where one blade produces more drag than the other, it will create a sideways force on the mast (the 'axle' that drives the rotor around), which could impart a significant stress on the structure. Of course you can combat this by making all the parts beefier - but that will also makes everything heavier which is something you generally don't want in an aeroplane. WegianWarrior (talk) 17:09, 28 February 2013 (UTC)


 * Thank you - again a very high quality response that teach me some of the fundamentals I was asking about. All of my questions are purely theoretical / meant to help me understand aerodynamics.  Going back to the video on human-powered helicopters (  http://www.youtube.com/watch?v=MkZ2bTWvRns  ) I do notice that the blades are held away from the center by a simple structure of very low drag.  If we must use rigid wings, could you talk about the stresses that would occur if the wings are in fact like a sheath on such a structure (when flying as a glider - i.e. the structure is unexposed), but to make the kind of makeshift "helicopter" can be pushed off to expose that structure in the center and escape the high-drag stall area?  (i.e. to look like the video of the human-powered structures)?  For this part of the question assume that one wing can magically flip to face the other direction.


 * Next, can we talk about what makes wings so asymmetric? Even a flat structure can generate lift (paper airplane) so it seems like the angle of attack is the most important thing?  How much additional lift does the special profile that makes it asymmetric really generate in addition to the lift that comes from angle-of-attack?


 * Thirdly - again, no practical application here, just trying to understand aerodynamics here: I notice that my original link to http://en.wikipedia.org/wiki/Eta_Aircraft_eta shows wings that are clearly "left" or "right" due to the bend at the end. Are there other difference between left and right?  That is to say, if you took a "left" wing, turned it around remaining horizontal (yaw it around) then would it now resemble the "right" wing except for having the turn on the end the wrong side, and be facing the wrong direction?


 * Finally, I have no practical interest, it is just to further my understanding of aerodynamics, and therefore I have no idea what a deformation would mean. I am just interested in the theoretical properties here.  That said what is to keep sections of a wing from turning to different angles with a locking mechanism inside?  It does not seem like it necessarily adds all that much weight: if we posit some kind of low-density beam-like structure going along the length of the wing, isn't it rather easy on a theoretical (not practical) level to attach different sections of the wing at different angles?  What I mean is that if instead of having to do it practically, and mid-flight, instead it was on the ground and somebody switched it manually from a fixed-angle configuration to tapering angles, what makes it inefficient to imagine independent sections that make this possible?   Please don't think that I have anything like this in mind: I am just trying to understand the basic fundamentals of wing design and aerodynamics here.  If, through whatever structure, it were possible to, say, independently position the wing in sections (let's say 20 of them) then would this alone be sufficient to at least get to a mostly-optimal "right" helicopter rotor (for counter-clockwise rotors), if that is the one that is going to continue to turn toward the wind?  Or would it still be a bad helicopter rotor for other reasons.  I do realize this wouldn't help the "left" wing which is now supposed to generate lift in the other direction, since as you said it is not symmetrical.  I am just curious if sections would at least help with the AoA issue, or, if not, then why?


 * Thank you so much for taking the chance to improve my understanding of these basic aeronautics concepts. --91.120.48.242 (talk) 17:41, 28 February 2013 (UTC)


 * Every rotary wing (helicopter rotor, aircraft or ship propeller, household fan...) has the same problem: airspeed too high at the tip and airspeed too low near the hub. If you look at most airplane propellers, you will see that the angle of attack changes from hub to tip to partially compensate for this. This gives fixed wings an efficiency advantage over rotary wings. --Guy Macon (talk) 22:16, 28 February 2013 (UTC)


 * Alright, but there are a bajillion ways to change something physically. (Something esoteric: shape memory materials), including just physically.  If we take a normal glider wing that is in sections, and manually (for the sake of argument) rotate and fix the sections to have different angles of attack, and perhaps push the start of the wing to be a bit away from the center (as in the designs here - http://www.youtube.com/watch?v=MkZ2bTWvRns - where the wings are held away from the center of turn), then is the new wing something like optimal for a helicopter rotor?  Or are there STILL going to be issues that make it completely wrong on a theoretical aerodynamic basis?  (Not a practical basis - I'm not even suggesting a mechanism for turning the Angle of Attack of the different sections).  If there are still issues, what are they?  I am just trying to increase my theoretical understanding, thank you. 91.120.48.242 (talk) 11:24, 1 March 2013 (UTC)

Organic chemistry - Flavons and Flavoniods
Are Flavons and Flavonoids the same thing? — Preceding unsigned comment added by 79.183.98.234 (talk) 17:03, 28 February 2013 (UTC)
 * Does "Flavons" refer to Flavones or Flavins? (+)H3N-Protein\Chemist-CO2(-) 17:45, 28 February 2013 (UTC)
 * Flavones are a subclass of Flavonoids. I have no idea what a Flavon is, but Wikipedia says its a little village in Northern Italy.  -- Jayron  32  17:47, 28 February 2013 (UTC)
 * ( Sorry about the edit conflict. ) "Flavon" is a single typo removed from both Flavone and/or Flavin. I suspect they tried to look for an article on "Flavons" and didn't quite find what they were looking for.  (+)H3N-Protein\Chemist-CO2(-) 17:56, 28 February 2013 (UTC)
 * "Flavon" is a song by Elton John. "Flavin" was a patron of Cheers. μηδείς (talk) 22:20, 28 February 2013 (UTC)

An optical distortion?
Hi,

on this picture there is an elliptical distortion;

Was it created by a filter or by an optical phenomenon?

Exx8 (talk) 17:56, 28 February 2013 (UTC)
 * Looks like it was made using a fisheye lens. Looie496 (talk) 17:59, 28 February 2013 (UTC)
 * It could also have been simulated after the fact with a tool like hugin. -- BenRG (talk) 18:01, 28 February 2013 (UTC)
 * X2 - When in doubt, check the EXIF data (which in this case has been wiped). It does however have the photographers name (someone named "MICHAEL KAPPELER") and mailing address embedded in it. But yes, it was obviously either taken with a fisheye or photoshopped to look like it was taken with a fisheye. The lack of actual EXIF data suggests it may have been the later. (+)H3N-Protein\Chemist-CO2(-) 18:08, 28 February 2013 (UTC)
 * The original image can be found here still lacking real EXIF data. But a quick survey of his gallery shows a fair number of photos taken with very wide lenses, so I'm leaning towards it not being a stitched panorama.  Hard to ever be 100% sure. (+)H3N-Protein\Chemist-CO2(-) 18:16, 28 February 2013 (UTC)