Wikipedia:Reference desk/Archives/Science/2017 February 28

= February 28 =

Auditory preparedness
Although my recent hearing test was good (in earbuds I can even hear The Mosquito alarm), I sometimes can't hear my own phone ringing in another room (and even in my own pocket when outside, so I often set it to vibration when I'm outdoors). Background noise apart, I suspect it's partially because the brain is unprepared to pick up the signal and as such stays unfocused, whereas when I'm listening something purposefully, it's prepared. Does any source discuss this issue? Brandmeistertalk  16:12, 28 February 2017 (UTC)


 * I believe general concepts like Acclimatization, Neural adaptation or even Attention cover the concepts you are getting at. -- Jayron 32 16:34, 28 February 2017 (UTC)


 * Note that the reverse is also possible. I keep hearing my phone ring when it hasn't, since the part of my brain searching for that auditory signal has too low of a threshold for a match.  See phantom ring. StuRat (talk) 17:41, 28 February 2017 (UTC)


 * I had this stuff too, but not frequently (including hearing someone calling my name when in fact there were other words/phrases). Brandmeistertalk  17:57, 28 February 2017 (UTC)


 * Yes, this is a general feature of an overactive pattern recognition system. Seeing faces in random objects is another, such as the "monkey face on Mars".  Another example is how hyper-sensitive my skin becomes when I see a mosquito. StuRat (talk) 18:01, 28 February 2017 (UTC)
 * Like topics on the TV series Brain Games (National Geographic). ←Baseball Bugs What's up, Doc? carrots→ 21:06, 28 February 2017 (UTC)
 * I wonder if you are referring to inattentional deafness? See BbBrock (talk) 22:04, 28 February 2017 (UTC)

Water pressure and volume under the sea and at surface
If you took a litre of water from the bottom of the Mariana Trench and brought it pressurised to the surface and depressurised it, what would be the volume of the water at sea level? --129.215.47.59 (talk) 17:52, 28 February 2017 (UTC)


 * Not much more. From Properties_of_water: "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume.".  The Mariana Trench is up to around 11 km deep, so it would compress a bit more than 1.8%.  StuRat (talk) 17:55, 28 February 2017 (UTC)


 * However the saturation-ability changes with pressure and since ocean water is far from being pure H2O. Water can for example solve up much more CO2 unter pressure and thus the moment you would depressure it, the exess CO2 would dissolut emidiately. This is a well known deadly danger for divers who depressure to fast. --Kharon (talk) 18:43, 28 February 2017 (UTC)


 * The lede to the article Mariana Trench mentions that at the bottom of the trench the density of water is increased by 4.96%. So a liter of water brought to the surface, after depressuring and out-gassing, would occupy 1,049 cc. Blooteuth (talk) 19:23, 28 February 2017 (UTC)


 * I believe you mean 1,000/(1&minus;.0496), which is 1,052 cm&sup3; (to the nearest whole unit). --76.71.6.254 (talk) 22:28, 28 February 2017 (UTC)


 * Perhaps he meant to use the original, slightly-incorrect-but-mostly-correct value: $\frac{1}{1-x} \approx 1+x$... this multiplicative inverse replacement is perhaps the most commonly-used Taylor series truncation in all of physics! Nimur (talk) 22:51, 28 February 2017 (UTC)




 * Why would the deep sea water be saturated with CO2? You would need some mechanism to make the concentration of CO2 (in grammes per kilogramme of sea water) in the deep water about 2000 times higher than in surface water, where partial pressure of CO2 is only about 41 Pa (which is the atmospheric CO2 pressure). Only volcanic activity or anaerobic decomposition of organic material could do such a thing. We don't see CO2 bubbles rising in areas where deep water rises to the surface. Of course, in lakes this can happen: see limnic eruption. PiusImpavidus (talk) 10:53, 1 March 2017 (UTC)


 * My understanding of our article oceanic carbon cycle is that CO2 gets absorbed by phytoplankton in the ocean surface (i.e. where photosynthesis is possible), and some of the organic matter generated there falls as solid sediments down to the ocean floor. It seems therefore possible that CO2 concentration at the bottom of the sea is made higher (by anaerobic decomposition of organic matter) than at the surface because of that transfer. (Could not find a source to prove or disprove this in 30s of web search, but surely there is some research out there) Tigraan Click here to contact me 14:35, 1 March 2017 (UTC)


 * Vulcanism, such as hydrothermal vents, is another possible source. StuRat (talk) 14:43, 1 March 2017 (UTC)


 * You got me wondering whether there is such a thing as CO2 saturation at that depth. I'm looking at  which speaks of Henry's law - apparently the equilibrium constant for CO2 in water is 29.41 atm/M, i.e. the concentration is the partial pressure in atm divided by 29.41 liter atmosphere mole-1.  For the deepest trench this is >1000 atm/29.41 = >33 molar.  But liquid carbon dioxide has a density of well under 1 g/cm, so there can't be more than 1000/44, i.e. less, moles in pure liquid carbon dioxide.  So either the water and the CO2 form different phases or they are miscible.  According to  they're not fully miscible (the CO2 is nonpolar, but I was thinking it might form hydrogen bonds).  So there should indeed be a saturation point.  Eventually I happened on  which reviews that liquid CO2 over a tenfold range of concentrations is soluble to about 5% w/w in water, which is reduced 1/5 in seawater (the salt makes water more hydrophilic, as ironic as that seems to say).  So AFAICT if you take CO2-saturated seawater from the depths, about 4% of its near-fixed volume is CO2, and you get maybe 40 grams of CO2 per liter of water, which (being about a mole) expands to the usual 22 liters at atmospheric pressure.  Impressive, but not as apocalyptic as I might have imagined.  (Unless I fouled up somewhere...) Wnt (talk) 15:20, 1 March 2017 (UTC)
 * Actually liquid carbon dioxide varies in density quite a lot with pressure and temperature, and I suspect it will have density greater than 1 in these conditions. But that does not change your argument anyway. More questions raised are what actually is the concentration of carbon dioxide at these depths? And can any living organisms survive the carbon dioxide concentration? Graeme Bartlett (talk) 22:27, 1 March 2017 (UTC)
 * How's this for cool? A picture of liquid CO2 droplets at Mariana Trench!  So it can go that high, and this creates... a "natural laboratory where the effects of carbon dioxide on marine organisms can be studied".  What those effects are I still don't know... nor what the concentration is far away from those vents.  Sigh... and now I see StuRat had that picture up already! Wnt (talk) 00:48, 2 March 2017 (UTC)