Wikipedia:Reference desk/Archives/Science/2016 December 26

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December 26

stupid NMR question

It is easy for me to think I understand proton nuclear magnetic resonance. Yet when it gets down to the nitty-gritty of just why J-coupling works as it does... I realize that my thoughts are not in order. Specifically...

• I understand that alcoholic (-OH) protons and other rapidly exchanging protons are in rapid equilibrium with other molecules in solution, and that a "D2O shake" can remove them from the NMR. But what prevents them from coupling with nearby protons? I have the impression that at least old fashioned NMR worked with a continuous wave where the spin flips of protons in a large population of molecules were measured without any sort of special pulse and decay regime at all. And I would tend to assume that an individual radio photon strikes a molecule instantaneously, taking a snapshot that should vary depending on whether nearby hydrogens are flipped one way or the other, shielding or deshielding. So the more I think of it, the more I'm not getting why spin-spin splitting doesn't affect those positions. Where am I going astray?

• The other thing that is confusing me is when NMR coupling works through multiple bonds - sometimes as many as four in conjugated dienes. What exactly is pushing on what, that allows a nucleus with a certain spin at one end to affect the stability of a nucleus at the other?

• I know there are other sophisticated NMR strategies that work from nucleus to nucleus. I still don't really understand though what the key differences are that determine when the relevant path is as a crow flies vs. along the bonds.

Wnt (talk) 02:58, 26 December 2016 (UTC)

The change does not happen instantaneously, or if it does we do not know when it happens. This will blur out any protons that are doing something else active, such as exchanging with the solvent. Protons may couple with other nearby protons, but if they are in random places, such as a liquid, there will not be a clearly defined line to go with it. Graeme Bartlett (talk) 22:57, 29 December 2016 (UTC)

@Graeme Bartlett: I'm not sure, but I think I'm getting you. If a compound emits a radio photon (I was since looking at how even the old CW instruments worked, and I realize now they were measuring emission, while an orthogonal coil input radio energy) then that photon has a frequency of some number of MHz, and it probably spans some wavelengths. Consistent with that, I found this which talks about a water hydrogen being detectable if it is exchanged less than once per 0.3 nanoseconds, which I would think is about a 300 Mhz instrument. It is very peculiar in my mind to think of photons-in-formation having a sort of average amount of gooey EM energy spooned into them before they are ready to bud off and take to the ether, but I imagine it is a productive heuristic to have in reach. Now if only you could explain why nuclei talk to each other via chemical bonds, I'd be on a path to having a clue, I think. Wnt (talk) 23:23, 29 December 2016 (UTC)

You can use the Heisenberg's uncertainty principle if you think of them as photons. But it would just be the inverse frequency period relationship. The time required is inversely proportional to the line width. Line widths are on the order of 100's Hz so you would need at least milliseconds to get a sharp line. I think of the coupling as magnetic fields. In the multiple bond an electron is delocalised over the chain of atoms, so causing a magnetic change along it causes a current to flow that might change something else on the chain. Graeme Bartlett (talk) 23:57, 29 December 2016 (UTC)

boat that can "fly" underwater like a penguin

Hi! When penguins swim underwater it looks a bit like they are flying. As a kid I wanted to have or build a submarine that uses a similar technique. Does something like that exist? Basically a seabreacher with wings. (((The Quixotic Potato))) (talk) 10:32, 26 December 2016 (UTC)

More like an aeroplane than an penguin, but the DeepFlight Challenger and Necker Nymph is/was positive buoyancy submersible crafts using hydrodynamic forces to descend. WegianWarrior (talk) 10:51, 26 December 2016 (UTC)

It is not an effecive principle for flying or swimming machines or vehicles (planes, drones, submarines) to use wings for propulsion. While is is an obviously implemented near perfection methode used in nature in many forms, see Tradeoffs_for_locomotion_in_air_and_water#Hydrodynamic_principles, the only methode really established in technology is gliding. In air this is well established by the principle of Lift (soaring)-planes and in water only by drones that use buoyancy-based propulsion, tho in that case it is very slow. So the answer is no and it wont work well until engeneering manages to build something as usable, fuleable, effective and capable as nature achieved by "inventing" the Muscle. --Kharon (talk) 16:04, 26 December 2016 (UTC)

The muscle doesn't exist that even comes close to the size, strength, speed, or efficiency of hydraulics/pneumatic actuators. The reason that flapping wings are not used by aircraft or watercraft is that rotary motion, which is (mostly) not available to organisms (but see Rotating locomotion in living systems), is generally more efficient than flapping motion. --Guy Macon (talk) 22:23, 26 December 2016 (UTC)

The octopus, for example, uses jet propulsion, which would seem to be superior to flapping of wings underwater. But even so, as you say, machinery easily beats them all. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:22, 27 December 2016 (UTC)

@Guy Macon. It seems you dont understand the challenge of an technological implementation. Even some electrical actuator that is build with High-temperature superconductors that get close to 99% efficiency, with whatever you pick in materials and engineering as mechanics and whatever energy source you add, with no budget limitations, you will not beat nature in efficiency in the end. Dolphins are capable to exeed speeds of 35 knots underwater without the need of a nuclear reactor, a rocket engine or alike. They eat 50 fish and travel 35 knots for one week on that. Technological implementation is not about single parts, like "your" efficient actuators, but the working concept you can build and its versatility in reality. --Kharon (talk) 04:36, 27 December 2016 (UTC)

Oh great, nutcase time. OK, I was mechanical engineer in charge of the design of a motor that was measured at 98.4% efficiency. No superconductors, no magic. You can even buy them in kit form for about $1500 for powering solar cars. How big are these 50 fish that a dolphin can travel at 35 knots for one week, ie about 7000 km? The main reason that wing-like propulsors aren't used is that screws are quite efficient (80% is not atypical) and very easy to drive mechanically. Wings require complexities in their drive that are not justified by any increase in performance, if there is one. Greglocock (talk) 08:00, 27 December 2016 (UTC)

I prefer the phrase "factually challenged". Muscles top out at about 30% efficiency. See Muscle#Efficiency. Atlantic bottlenose dolphins in an ambient seawater pen eat about 100,000 kcal/week.[1] On average an adult dolphin will eat four to nine percent of its body weight in fish daily, so a 550 lb dolphin will eat 22 to 50 pounds of fish per day.[2] Yes a dolphin can cover long distances running off of stored body fat, just as my car can cover long distances on a full tank of gas, but that says nothing about fuel efficiency. And by the way, we were building machines that could travel underwater faster than any dolphin back in WWII -- no superconductors required. Nowadays we can go a lot faster. See Underwater speed record. --Guy Macon (talk) 08:31, 27 December 2016 (UTC)

FWIW:[3][4] Wnt (talk) 12:24, 27 December 2016 (UTC)

In those cases, stealth would be the overriding factor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:55, 27 December 2016 (UTC)

Does anybody know what flying fish do with their large pectoral fins when they are underwater. Are they used in propulsion which would link to the OP, or perhaps they keep them folded against the body for streamlining? DrChrissy ^(talk) 20:17, 27 December 2016 (UTC)

Not a flying fish, but "We examine underwater flight in the spotted ratfish (Hydrolagus colliei) to test the model. This animal relies entirely on flapping its large, flexible pectoral fins for routine locomotion"[5] DrChrissy ^(talk) 21:29, 27 December 2016 (UTC)

@DrChrissy: Here's [6] a video showing a flying fish using a few flaps for low-speed maneuvering in shallow water. I don't think they use the wings much to flap while swimming at speed. Here [7] you can see them taking off, and in the first few seconds it's pretty clear the wings are held flat against the body during the high-speed thrust phase just prior to launch.

Here [8] is a very nice review article of swimming modes, with an eye toward energetics and engineering. Figs. 14,15, and associated refs will be interesting to User:The Quixotic Potato. The key term for this "swimming like flying with 'wings' is labriform swimming, that should help future searches, here's a few top hits in the academic literature [9] [10]. Here's another paper specifically about the energetics of penguins and ducks that use wings under water [11]. While most dabbling ducks keep their wings folded while under water, many diving ducks use their wings to fly downward more rapidly, example here [12]. SemanticMantis (talk) 21:24, 28 December 2016 (UTC)

Thanks so much for this. Wonderful references and videos. (some WP articles clearly need this information) In the video about the diving ducks, I loved that they use their wings to dive, but kept them tucked in when rising to the surface. Presumably they can rise quicker by remaining stream-lined. By the way, in my research for this question, I read somewhere that flying fish tuck their pectoral wings in both before exiting and re-entering the water. I imagine this is due to the risk of injury. DrChrissy ^(talk) 21:44, 28 December 2016 (UTC)

Awesome, thank you. I don't think I've ever read the word "labriform" before! (((The Quixotic Potato))) (talk) 08:05, 29 December 2016 (UTC)

OP here, thank you all. This is why I love Wikipedia. I wish I would've had access to Wikipedia as a seven year old, but it didn't exist back then (and I didn't even have internet access). Very interesting stuff, I'll spend a couple of days reading everything and everything that those pages link to. I have to admit that my seven year old self didn't really care about fuel efficiency. DrChrissy's question also made me curious. (((The Quixotic Potato))) (talk) 06:07, 28 December 2016 (UTC)

Nah i did not argue about fuel efficency - thats unfair because we use fuel like gasoline that contains 42.4 MJ/kg while meat only contains 16.8 MJ/kg. Also human enineering has no problem exeeding speeds or ranges common in nature. No animal will ever reach the moon or fly at Mach 15 on its own. Yet engineering still can not copy nature and build selfsufficient machines small as a penguin or a bottlenose that can travel around the world all on its own in equal speed and is capable of acrobatic moves. Just like in robotics they are still trying to copy a human hand and that is what i meant with "efficiency in the end" as an complete concept. Again technological implementation is not about single parts and that was how i understood your question. A submarine that can move like a penguin. Maybe in 200-500 years engineering will be capable to build something alike but currently engineering remains outclassed by natures "inventions". --Kharon (talk) 12:54, 30 December 2016 (UTC)

Deposit of fog droplets vs. fog drip

The original definition by the WMO of deposit of fog droplets was: "deposit of non-supercooled fog or cloud droplets on objects the surface temperature of which is above 0°C. Observed especially in mountainous areas where orographic clouds are frequent. The intensity of the deposit depends on the duration and granulometry of the fog (or clouds) and on the speed of impact of the droplets. It is also a function of the wettability and interception coefficient of objects (paticularly high for conifer needles). When this phenomenon is high, the droplets can run together and drip on to the ground. In some cases the amount of water falling from branches during a single night could be the equivalent of a moderate rainfall" (International Cloud Atlas vol.1, 1975, p. 115 – some words and phrases were changed by me for copyright issues). Although this definition may be similar to fog drip, it seems also to include the moist deposit of fog droplets on the ground falling directly from the fog itself. The new definition that can be read in this draft seems to include only fog drip from clouds. I would like to know why moisture from the fog itself it is not often considered in those definitions.--Carnby (talk) 11:26, 26 December 2016 (UTC)

information on a french reflecting circle by lorieux, lepetit

Hello, I would like any information regarding a french reflecting circle by lorieux, lepetit. Any help would be greatly appreciated. Thank you in advance. — Preceding unsigned comment added by Anthony Sura (talk • contribs) 12:21, 26 December 2016 (UTC)

Have you seen Reflecting instrument#Reflecting circle? Looie496 (talk) 14:39, 26 December 2016 (UTC)

See FRENCH REFLECTING CIRCLE by "LORIEUX, LEPETIT N° 254". Blooteuth (talk) 23:39, 26 December 2016 (UTC)

Are the waves of the ECG created before the real contraction of the heart?

Normally medical staff (according to what some of them told me) are said that the depolarization waves of the ECG represent the contraction of the heart, but I've read in the past that the ECG waves of depolarization happens in fact before the contraction, but because it happens in milliseconds then it's negligible and nobody talks about it. Is that true? I'd like to see any source which support it (Unfortunately I don't find the place that I've read it) 93.126.88.30 (talk) 17:49, 26 December 2016 (UTC)

Typical action potential in a ventricular muscle cell

It might (or might not) help to look at our cardiac action potential article. As you can see in the diagram I've inserted, a typical action potential in a heart muscle cell has a very fast onset and then a long sustained phase. The QRS complex in the ECG reflects the onset, but contraction occurs throughout the long sustained phase. However without that fast onset the contraction would not be coordinated properly. I don't quite understand what you mean by "it's negligible and nobody talks about it". What does "it" refer to there? Looie496 (talk) 18:05, 26 December 2016 (UTC)

I think the OP is using "it" to mean the delay between the recorded electrical activity and the muscle activity. DrChrissy ^(talk) 20:13, 26 December 2016 (UTC)

Yes, this exactly what I meant. Thank you for the answer, but I didn't understand the sentence "The QRS complex in the ECG reflects the onset, but contraction occurs throughout the long sustained phase.". Can you point me please clearly on what parts in the diagram you mean?93.126.88.30 (talk) 07:51, 29 December 2016 (UTC)

The ECG picks up the electrical activity of the heart muscle itself, since there is so much of it, rather than any regulatory nerve (and indeed, the heart can beat without innervation). So when the ECG picks something up, the heart muscle cells are actually "contracting" in the sense of a physiological activity. To get to contracting in terms of physics, the route is slightly longer: the action potential allows the Ryanodine receptor 2 to join in bringing calcium to the cytoplasm, and that calcium interacts with troponin C, which is in a complex with myosin. And only after the myosin is allowed to act do the heart cells actually start getting shorter, which of course takes some time. Still, for not particularly surprising reasons, I'd hazard, this is one of the shorter and more foolproof examples of signal transduction that I can think of. Wnt (talk) 19:56, 26 December 2016 (UTC)

Determine whether caulk is silicone or acrylic?

Is there an easy way to determine whether a sealant caulk used around a window frame is silicone or acrylic? I want to use a remover but it's more troublesome to get an acrylic one so I'd like to figure out what will work in advance. Picture in case that makes a difference --79.69.193.153 (talk) 21:50, 26 December 2016 (UTC)

Do you have isopropyl alcohol? It is absorbed by acrylic caulk and softens it, making it easier to remove mechanically. I believe (but have not personally tested) that silicone caulk laughs at your puny isopropyl alcohol. --Guy Macon (talk) 22:29, 26 December 2016 (UTC)

Yes I do, that's perfect! Thanks! 79.69.193.153 (talk) 15:39, 27 December 2016 (UTC)