Wikipedia:Reference desk/Archives/Science/2023 March 18

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March 18

Mass-radius relationships for planets and the Birch–Murnaghan equation of state

Has anyone ever attempted to derive a general mass-radius relation for materials with specific parameters of the Birch–Murnaghan equation of state? I've seen lots of relations for different materials, but nothing that can be generalized. Jo-Jo Eumerus (talk) 10:38, 18 March 2023 (UTC)

@Jo-Jo Eumerus: Consult this paper. TrangaBellam (talk) 12:04, 20 March 2023 (UTC)

This question was better suited at Physics Stack Exchange; can we use Latex in wiki? TrangaBellam (talk) 12:05, 20 March 2023 (UTC)

@TrangaBellam:Help:Displaying a formula Jo-Jo Eumerus (talk) 15:05, 20 March 2023 (UTC)

Why do Zotepine and Amitriptyline appear flipped (180d turned over)?

Zotepine

Amitriptyline

Why do Zotepine and Amitriptyline appear flipped (180d turned over)? I mean, why Zotepine seems to go from bottom to top and Amitriptyline seems to go from top to bottom? Thanks. 2001:44C8:4400:884B:3510:3E81:2A7A:B4D6 (talk) 14:30, 18 March 2023 (UTC)

Illustrators preference. 2601:249:8200:A640:E5EE:B6CC:E3E1:BDF5 (talk) 15:16, 18 March 2023 (UTC).

I'm not sure what you mean. The two molecules shown have side chains attached at very different locations. The central ring structures are in the same orientation in both diagrams. Note that the most central ring has three sides pointing towards the top of the page and two sides pointing to the bottom of the page. --User:Khajidha (talk) (contributions) 17:42, 18 March 2023 (UTC)

I have edited the question to clarify what I meant to ask. 2001:44C8:440A:3C0:E9D1:8E95:916:C412 (talk) 18:04, 18 March 2023 (UTC)

Then the answer is probably to keep the central ring structure in the same orientation for ease of comparison between similar molecules. With perhaps a dash of the previously mentioned illustrator's preference. --User:Khajidha (talk) (contributions) 18:28, 18 March 2023 (UTC)

Hi, this is just something about illustration. If you mind the bottom and top, you can draw it on your Chemdraw and rotate it. -Lemonaka‎ 08:34, 20 March 2023 (UTC)

The main idea is that molecules are real objects, that can be represented from any orientation or perspective as most useful for a given context. Some fields of study have standards or preferences for the default, such as keeping the three rings of the core aligned. But it's interesting that the similar-looking chain is in a different place on these cores! Structure–activity relationship is an important type of analysis when looking at how the various parts of the structure behave to give an overall biochemical effect. Looking at our zotepine and amitriptyline articles, even the colorful 3D diagram at zotepine is visually flipped compared with the skeletal representation. At those articles, as with most of our chemical and drug articles, the infobox has a "3D model (JSmol) Interactive image" link that gives a VR model you can rotate without needing any special software. DMacks (talk) 08:50, 20 March 2023 (UTC)

When they add a canal how far along the coast can it change the tide and current tables?

If the tides at the ends are out-of-phase with each other and/or have different amplitudes. I imagine the effect gets diluted the further the canal is from your part of the coast. Sagittarian Milky Way (talk) 14:34, 18 March 2023 (UTC)

How many locks does your hypothetical canal have? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:10, 18 March 2023 (UTC)

It'd have to be one of those lockless canals. Sagittarian Milky Way (talk) 15:24, 18 March 2023 (UTC)

No practical artificial canal can be big enough to absorb or transmit a quantity of water sufficient to have any perceptible effect on the tide. If you want to look at natural canals that may have an effect, try the Solent (small scale), or the English Channel (large scale). -- Verbarson  ^talk_edits 23:42, 18 March 2023 (UTC)

I always wondered what would happen if a complete cut were made from one ocean to the other, somewhere in Panama. Without locks. (As a kid, that's how I imagined the Panama canal.) I know that in practical terms, this would take a lot of digging since there are mountains in the way, but let's assume it could be done. Is the sea level the same on both sides? Of course, if it isn't the same, then a lot of water would flow in one direction very fast, once the cut is finished. I wonder if this flow would ever stop, assuming a very wide canal. Could ships sail back and forth? So many questions... David10244 (talk) 09:32, 20 March 2023 (UTC)

These were concerns when Suez was first being dug, due to a faulty survey – see Suez Canal. In the Panama case, any difference in mean sea level would have been eradicated by flow around Cape Horn and around northern Canada. However the tidal issues might lead to a significant problem. The M2 (semi-diurnal moon-based) component is over a metre at the Pacific end of the canal and zero in the Caribbean. Suez only has a 10cm component at the sourthern end and zero at the north so the effects are negligible. Martin of Sheffield (talk) 10:16, 20 March 2023 (UTC)

It's quite possible that sea level is different on either side of Panama, but that wouldn't necessarily mean water would flow from one side to the other if they were connected. The height of mean sea level varies (relative to the ellipsoid that best approximates the shape of the Earth) due to variations in gravity. So if it is higher on one side, that's because gravity is pulling it there, so as far as the water is concerted it has already flowed "down" as far as it can go ("down" being defined as the direction gravity pulls). You might though get some flow due to prevailing winds, and the tide.Iapetus (talk) 10:25, 20 March 2023 (UTC)

I was surprised to read that the sea-level and lock-free Corinth Canal in the Mediterranean (which I thought had minimal tides) was troubled by tidal currents. -- Verbarson  ^talk_edits 10:55, 20 March 2023 (UTC)

Inasmuch as differences in sea levels play a role in inducing currents in a lock-free canal (or natural strait), the relevant measure is the difference in local sea levels with respect to the geoid. By definition, it is zero in the absence of winds and tides; local variations in gravity play no role. There may nevertheless be currents, not only tidal currents energized by a fluctuating difference in local sea levels, but for a canal connecting oceans also currents energized by oceanic currents. An open Panama Canal would definitely be influenced by the Equatorial Counter Current.  --Lambiam 13:32, 20 March 2023 (UTC)

The flow of water through the canal would depend on the level difference and length, width and depth of the canal. In case of a tidal level difference, the resonance frequency of the canal would matter too. For example, if there can be a seiche in the canal with a frequency matching the tides and a wavelength such that the length of the canal is 1/2+n times the wavelength, there will be no flow of water through the entrances of the canal if the tides at the endpoints are in counterphase and equal amplitude.

The Suez Canal has no locks, but tides are minor there. There's generally a slow northbound flow. From an ecological point of view, it had been better if there had been locks, limiting the flow that flushes Great Bitter Lake to keep that lake hypersaline to block species from migrating, especially as flow increased over the years as the canal was widened and deepened. Increasing the surface area of Great Bitter Lake would be a good idea too.

A sea-level Panama Canal has been proposed in the 1950s, using nuclear blasts to cut through the mountains (see Project Plowshare), but was cancelled for obvious reasons. It would have been an ecological disaster too.

But in any case, if the flow of water through the canal had been sufficient to significantly affect the tides around the endpoints, flow speed in the canal would have been too high for safe shipping and locks would have been added. Erosion would have been a problem too; you wouldn't want to canal to continue growing on its own. PiusImpavidus (talk) 11:04, 20 March 2023 (UTC)

Tides would affect navigation, principally with the depth changing. I would suggest though that such a canal might be modelled by rivers, where the limit of tides is the Caribean and the mouth the Pacific. Even with 5m ranges the flow up and down rivers rarely exceeds 3 knots. Martin of Sheffield (talk) 11:51, 20 March 2023 (UTC)

Current in the Hudson River (moderately shallower then Suez and several times wider) can reach almost 3 knots with less than 8 feet of maximum astronomical range, Cape Cod Canal (≤50% the width and depth and 6-7% the length of Suez) can reach at least 4.5 knots with only a few meters of tidal range (less range south of it than north). Hell Gate (part of a Corinth-like strait), New York City can reach 5 knots with less than 12 feet of maximum astronomical range at one approach and less than 8 feet at the other (about 90° out-of-phase). This is even with dredging, turbulence-producing rock exploding, Little Hell Gate (a tributary) plugging and other artificial hellness reduction (there's a brief low speed time twice a day as it flows like a lung). The entire strait its on is (modern chart) usually wider than Suez, very roughly as deep though variable, and 6-7 times shorter than Suez.Saltstraumen (Norwegian fjord mouth constriction) says 8 or 22 knots (sources differ) from only 1 meter of sea level difference. 3 km long and 0.15 km wide. Sagittarian Milky Way (talk) 15:25, 20 March 2023 (UTC)

Interesting. I note that today the tides at Sheerness are 0539(0.63), 1138(5.75), 1753(0.86) and 2355(5.59) – so let's take that as a mean tidal range of 4.9m. Lest I be accused of cherry-picking, a quick scan of the tide tables shows springs in a few days of 6.11 m. The chart shows tidal diamond M as having a maxiumum of 2.9kts, 3hrs after HW springs Sheerness. That is at the confluence of the Medway and Thames at The Nore. All of which goes to show that any modelling is complex. Since no-one is ever going to build a sea level canal across Panama, we'll never know! Martin of Sheffield (talk) 15:58, 20 March 2023 (UTC)

"Formation of the Isthmus of Panama" has some interesting looking references to modeling of the reverse. fiveby(zero) 18:32, 20 March 2023 (UTC)

Consider the Strait of Gibraltar linking the tidal Atlantic ocean to the essentially tideless Mediterranean sea. 37.171.124.195 (talk) 08:59, 22 March 2023 (UTC)