Wikipedia:Reference desk/Archives/Science/2018 September 12

= September 12 =

Jellyfish
Can you assume that there are no jellyfish in the sea after the summer months (I Mean now and in the next month). Is that something restricted to the summer? I have south Spain in mind, other places on the Mediterranean might be interesting. — Preceding unsigned comment added by 37.252.180.169 (talk) 03:24, 12 September 2018 (UTC)
 * There is a Spain Travel forum post on that subject; you might try a query there: —107.15.157.44 (talk) 05:57, 12 September 2018 (UTC) ... Reports that I could find regarding beach closures in Spain due to jellyfish are dated April & May (2018).


 * I have found some random comments in travel sites too besides anecdotal evidence provided by locals. But I was wondering from a more scientific point of view. Does winter decimate jellyfish populations? 31.177.99.137 (talk) 13:16, 12 September 2018 (UTC)


 * If there were no jellyfish in the sea at all, where would the next generation of them come from? ←Baseball Bugs What's up, Doc? carrots→ 10:57, 12 September 2018 (UTC)


 * I obviously mean on the sea shore. But even then, it might be possible that there's no specimen of some living being in winter, only eggs that will hatch in the next season. 31.177.99.137 (talk) 13:16, 12 September 2018 (UTC)
 * Thanks for clarifying. If it was obvious, I wouldn't have asked. :) ←Baseball Bugs What's up, Doc? carrots→ 13:21, 12 September 2018 (UTC)


 * In a sense, the next generation of jellyfish will come from polyps ! What we usually think of as a jellyfish is actually a jellyfish medusa - the final sexually reproducing phase in a complex life cycle. Medusae have relatively short lives compared to the polyps that bud them. Gandalf61 (talk) 13:24, 12 September 2018 (UTC)


 * "Patterns of jellyfish abundance in the North Atlantic" discusses reasons for seasonal variation of jellyfish in the North Atlantic. It looks as if in the open ocean, jellyfish populations peak with prey populations, whereas nearer shore (in the continental shelf area) they peak with surface temperature.  (The paper also states that in the shelf area "advection and aggregation" affect jellyfish population, and this appears to be advection and aggregation of prey, which leaves me puzzled.)--Wikimedes (talk) 07:16, 13 September 2018 (UTC)

Advances in consumer facing industries
Why is it that consumer facing industries such as automotive, retail, personal banking etc seem to advance faster than corporate industries such as legal, investment banking, construction etc especially in terms of IT and digital? Clover345 (talk) 06:33, 12 September 2018 (UTC)
 * Buisiness and government will want to enter into long term contracts, perhaps using tenders. They also want stability and assurance in their IT systems, so they don't just want to take whatever is the latest that will mean they needs to change instructions and cope with a new bunch of issues. Operating system changes for example mean that applications that use them have to be changed, and then retested. There is a lot of expense in changing unnecessarily. Some industries are very conservative and may be regulated to avoid changes. This includes aviation. Graeme Bartlett (talk) 09:49, 12 September 2018 (UTC)
 * I'd say manufacturers strive to make consumer products that look shiny but fall apart in a couple of year. Industrial equipment, on the other hand, is made to last, often some decades, and it normally does not matter how it looks. --31.177.99.137 (talk) 13:24, 12 September 2018 (UTC)
 * Planned obsolescence is the tradeoff for products being relative inexpensive. If you want an industrial-strength laptop PC, for example, you're going to pay a lot more than what you would get at Best Buy. Related to Project management triangle. ←Baseball Bugs What's up, Doc? carrots→ 15:22, 12 September 2018 (UTC)

Quantum CAP Theorem
What are the limits on syncing up distributed Quantum machine learning?

I.e. has anybody done the math on a quantum version of the CAP theorem?

In short, given a swarm of killer robots, how do you ensure that they all learn together?

Hcobb (talk) 14:08, 12 September 2018 (UTC)

Fluid dynamics question.
If you have water flowing down a vertical steel pipe, and both the water and pipe were at 25 C. Now, if both the water and pipe were at 50 C, water would flow faster, because of this thing called friction. Change in viscosity with temperature. So my question is, which would flow faster, if the water were at 25 C and pipe at 50 C, or water at 50 C and pipe at 25 C. As far as I know, there is no difference with water flowing in a horizontal pipe, only vertical pipe. Thanks. 12.239.13.143 (talk) 18:17, 12 September 2018 (UTC).
 * If we can assume laminar flow i.e. no cross-currents perpendicular to the direction of flow, nor eddies or swirls, and that the fluid is incompressible and Newtonian, the empirical Hagen–Poiseuille equation will be useful, see Hagen–Poiseuille equation. It requires knowledge of the liquid's dynamic viscosity μ which is a function of temperature shown at Viscosity. See the theoretical development of laminar Pipe flow at Hagen–Poiseuille_equation and Hagen–Poiseuille flow from the Navier–Stokes equations. DroneB (talk) 20:53, 12 September 2018 (UTC)
 * I don't see how this is useful, my question was about temperature and not pressure. And I am not comparing different materials with same liquids, or different liquids with same pipe materials. Only same liquid and same piping material. Either way, I think the answer I was looking for is: cooler pipe cooling the hotter water, or cooler water cooling the hotter pipe - whichever is slower. And whichever answer that is, what are materials where the opposite is true, for different piping materials. 12.239.13.143 (talk) 22:56, 12 September 2018 (UTC).
 * While DroneB did miss the point of your question, I do not see what their answer has to do with pressure. (I also strongly doubt Hagen-Poiseuille applies for reasonable values of pipe diameter and flow speed for water.) The answer does make a decent job of explaining why temperature impacts viscosity (which impacts friction) but your original post seems to acknowledge that.
 * Friction is driven by the (viscous) boundary layer in the liquid near the surface, so what matters is the water's temperature. Now, of course, thermal transfer between pipe and water means that "the water's temperature" can hardly be fixed different from the pipe's (even if you try, water temperature near the pipe will likely not be at the regulation temperature), and that thermal properties of the pipe will eventually matter; but good luck on quantifying such an effect. Tigraan Click here to contact me 11:28, 13 September 2018 (UTC)
 * This would be a pretty gnarly set of differential equations, one for heat transfer and one for flow, doable but tedious. In an ideal world where everything stays at a constant fixed temperature, you could set up a numerical solution with a computer program. In the real world, I suspect that the pipe and water would quickly come to temperature equilibrium, especially if the pipe is metal. shoy (reactions) 13:27, 13 September 2018 (UTC)
 * In order for the question to be "interesting but solveable" I would assume that the pipe is long and has large diameter...that means we have pretty good equilibrium of the pipe temp with the outer layer of water and a gradient towards the center that is at the supply temperature. That gets away from a pipe that is thin enough for temperature to equilibrate all the way to the center (making the question pointless). DMacks (talk) 15:26, 14 September 2018 (UTC)
 * I read somewhere that the maximum speed for rain drops is 19 mph. So does that mean, water falling down a vertical pipe - whether huge diameter like 10 meter, or 1 inch - neither water will fall more than 19 mph? I'd like to see some models for hot water falling down hot pipes vs. room temperature water falling down room temperature pipes, even for a pipe that could be an inch in diameter. 67.175.224.138 (talk) 16:27, 15 September 2018 (UTC).
 * Err... No. The maximum speed of raindrops is limited by air friction. (More precisely: the size of raindrops is lower than a couple of mm because of surface tension effects, and then for a given size there is a terminal velocity where air friction compensates gravity.)
 * In pipes, unless something goes wrong, there is water everywhere so it is not like water "drops" in the usual meaning of the term. Water is pushed around by pressure differences, and gravity makes pressure higher at the bottom of a water column than at the top, so for a given pumping pressure you can send water faster downwards than upwards, but it is conceptually not at all similar to "falling". Tigraan Click here to contact me 09:18, 19 September 2018 (UTC)


 * According to the viscosity of water in different temperatures as listed here, the change is much more significant if the water temperature changes. Additionally Hagen–Poiseuille equation focuses on pressure, which is not very helpful for estimating flow speeds, because the actual limits on flow speed doesnt lie in pressure but in already mentioned flow state (laminar/turbulent) which in Fluid mechanics is measured/calculated in/by the Reynolds number which is better aka implies less resistance and thus faster flow for higher viscosity (as long as its not a Non-Newtonian fluid, which luckily (else flow is getting very complicated) water is only in its Slush-state. --Kharon). (talk) 11:26, 16 September 2018 (UTC)

Desire to raise legs
I am familiar with restless legs syndrome, albeit only from descriptions, and am almost certain that I am not talking about it!

Is there a name for the seemingly inexplicable desire to raise one's legs? Specifically, to a higher level than one's torso when lying down.--Leon (talk) 21:12, 12 September 2018 (UTC)
 * That's a new one, unless you're elevating them for circulation reasons. What have you found on Google so far? ←Baseball Bugs What's up, Doc? carrots→ 22:31, 12 September 2018 (UTC)


 * You might mention that to your doctor. If you also feel faint when you stand up, that is orthostatic hypotension and could be related.  I've seen it claimed that sleeping with your head elevated is good for many reasons, so instinctually doing the opposite sounds slightly amiss.  ObIncantation: we can't give medical advice here bla bla.  173.228.123.166 (talk) 06:50, 13 September 2018 (UTC)
 * Leon is not looking for medical advice, he is not even saying that he has a medical complaint. I wonder why anyone would suggest he see a doctor or suggest that the condition he asks about is "slightly amiss". I have been in nursing most of my life and have never encountered the idea that sleeping with your head elevated is good - although it is customary. Richard Avery (talk) 13:06, 13 September 2018 (UTC)
 * The OP should speak for himself. ←Baseball Bugs What's up, Doc? carrots→ 13:10, 13 September 2018 (UTC)
 * I'll speak for myself - I corroborate with Richard. I'm just curious. I'll add that this desire seems to be coupled with a general desire to get into strange bodily positions, but what I have already described is the most obvious manifestation of this.--Leon (talk) 16:17, 13 September 2018 (UTC)
 * Where have you seen this? ←Baseball Bugs What's up, Doc? carrots→ 18:13, 13 September 2018 (UTC)


 * If not circulatory maybe it's psychological, from some kind of anxiety? Regarding thing about sleeping with head elevated, here's an example:.  Obviously not RS but it's an example of some of the (possibly bad) info that's out there.  Actually a quick web search shows the author is a "medical anthropologist" who writes lots more such unorthodox stuff.  So skepticism is warranted. 173.228.123.166 (talk) 17:01, 13 September 2018 (UTC)