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September 20 Information
Onions
Onions famously come in layers, with the outermost layers being a dry, papery consistency, while the inner layers are fleshy (and delicious). Now I believe I've seen layers in-between these two states, so I assume they start out basically the same. Is that correct? If so, what process is turning the thick layer into the papery state? It's apparently not simple desiccation, as the thin versions seem to be largely immune to water, and cannot be re-hydrated... --
Stephan Schulz (
talk)
12:12, 20 September 2022 (UTC)reply
Here you can read a highly technical description of the biochemical changes that accompany the drying of the outer scales – which already begins in a relatively early stage of bulb growth. I don't know what sometimes triggers more inner scales' going down the same path; perhaps some disease that leads to premature cell senescence. --
Lambiam15:22, 20 September 2022 (UTC)reply
The pressure depends only on the weight of the water column (and atmospheric column, if you are particular) directly above any particular parcel of water. If you find that hard to imagine, consider a plexiglass cone, open in the bottom, in a bath tub. If there was a pressure differential at the bottom of the cone, there would be a continuous flow, and you'd have a nice
perpetuum mobile. This is physically somewhat unlikely ;-). So there is no differential. And why should that change if you close off the bottom? --
Stephan Schulz (
talk)
16:28, 20 September 2022 (UTC)reply
The effect of a narrowing cone-shaped restriction on a pressure wave travelling in a fluid is to increase its pressure so adding a cone can usefully increase the sensitivity of a hydrophone. However the presence of a rigid cone anywhere in a fluid
Pressure gradient that gravity has established makes no difference to the vertical pressure distribution. The pressure at the bottom of the cone described by the OP depends only on the depth of communicating layers of sea water above. The geometry of connections between the layers is actually irrelevant so there can be convoluted horizontal channels and not all water need be directly above.
where ρ is the fluid
density (kg/m3), g is
gravitational acceleration (m/s2), H is the total height of the liquid column and patm is the
atmospheric pressure. This can be visualized as a
pressure prism. The only difference between the forces exerted by fluid pressure on unit areas of a vertical wall, a sloping wall, floor or submerged ledge is the direction of the force vectors.
Philvoids (
talk)
18:38, 22 September 2022 (UTC)reply
The
Challenger Deep south of Japan extends as deep as 10,920 ± 10 m (35,827 ± 33 ft). The
ROV Kaikō measured temperature (water temperature increases at great depth due to adiabatic compression), salinity and pressure values 2.6 °C (36.7 °F), 34.7‰ and 1,113 bar (111.3 MPa; 16,140 psi). I find no data to suggest that strongly covalent silicon dioxide SiO2 the constituent of silica sand and quartz is soluble in those conditions. However silica might dissolve, possibly to
Silicic acid, in these cases:
hydrothermal vents raising superheated water that is known to dissolve quartz. That is the basis of a useful industrial process to obtain pure quartz crystal that forms when the solution cools.
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a
transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the
current reference desk pages.
September 20 Information
Onions
Onions famously come in layers, with the outermost layers being a dry, papery consistency, while the inner layers are fleshy (and delicious). Now I believe I've seen layers in-between these two states, so I assume they start out basically the same. Is that correct? If so, what process is turning the thick layer into the papery state? It's apparently not simple desiccation, as the thin versions seem to be largely immune to water, and cannot be re-hydrated... --
Stephan Schulz (
talk)
12:12, 20 September 2022 (UTC)reply
Here you can read a highly technical description of the biochemical changes that accompany the drying of the outer scales – which already begins in a relatively early stage of bulb growth. I don't know what sometimes triggers more inner scales' going down the same path; perhaps some disease that leads to premature cell senescence. --
Lambiam15:22, 20 September 2022 (UTC)reply
The pressure depends only on the weight of the water column (and atmospheric column, if you are particular) directly above any particular parcel of water. If you find that hard to imagine, consider a plexiglass cone, open in the bottom, in a bath tub. If there was a pressure differential at the bottom of the cone, there would be a continuous flow, and you'd have a nice
perpetuum mobile. This is physically somewhat unlikely ;-). So there is no differential. And why should that change if you close off the bottom? --
Stephan Schulz (
talk)
16:28, 20 September 2022 (UTC)reply
The effect of a narrowing cone-shaped restriction on a pressure wave travelling in a fluid is to increase its pressure so adding a cone can usefully increase the sensitivity of a hydrophone. However the presence of a rigid cone anywhere in a fluid
Pressure gradient that gravity has established makes no difference to the vertical pressure distribution. The pressure at the bottom of the cone described by the OP depends only on the depth of communicating layers of sea water above. The geometry of connections between the layers is actually irrelevant so there can be convoluted horizontal channels and not all water need be directly above.
where ρ is the fluid
density (kg/m3), g is
gravitational acceleration (m/s2), H is the total height of the liquid column and patm is the
atmospheric pressure. This can be visualized as a
pressure prism. The only difference between the forces exerted by fluid pressure on unit areas of a vertical wall, a sloping wall, floor or submerged ledge is the direction of the force vectors.
Philvoids (
talk)
18:38, 22 September 2022 (UTC)reply
The
Challenger Deep south of Japan extends as deep as 10,920 ± 10 m (35,827 ± 33 ft). The
ROV Kaikō measured temperature (water temperature increases at great depth due to adiabatic compression), salinity and pressure values 2.6 °C (36.7 °F), 34.7‰ and 1,113 bar (111.3 MPa; 16,140 psi). I find no data to suggest that strongly covalent silicon dioxide SiO2 the constituent of silica sand and quartz is soluble in those conditions. However silica might dissolve, possibly to
Silicic acid, in these cases:
hydrothermal vents raising superheated water that is known to dissolve quartz. That is the basis of a useful industrial process to obtain pure quartz crystal that forms when the solution cools.