Wikipedia:Reference desk/Archives/Science/2019 December 10

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December 10

Is there a qualitative explanation for avoided crossing ?

So I have not been allowed to take quantum chemistry in my program due to silly bureaucratic rules based on academic caste. As such, I plan to teach myself the core ideas after finals. However, how does avoided crossing lead to resonance stabilization using qualitative frontier molecular orbital theory? I can't find any good sparknotes on this topic online. Yanping Nora Soong (talk) 00:32, 10 December 2019 (UTC)

Avoided crossing is a specific episode related to the non-crossing rule (two eigenvalues corresponding to orbital of the same symetry cannot cross even though the corresponding two diagonal matrix elements can cross, see Woodward–Hoffmann rules for context ). This discussion on state correlation and orbital correlation illustrates the occurrence of avoided crossing. An absolutely similar example of electrocyclic reactions is used in the FMOA article, so is still leaving it to you to establish a qualification. More succintly, see this State Correlation Diagram in a pericyclic reactions context. --Askedonty (talk) 22:21, 13 December 2019 (UTC)

Subsidence

Are there any famous examples of subsidence of structures built on pad foundation? Maybe houses? 2A01:4C8:28:AD02:404:9DC:2956:7D76 (talk) 21:32, 10 December 2019 (UTC)

Not sure exactly what pad foundation is, but the leaning apartment blocks of Santos might qualify. 93.136.71.134 (talk) 21:38, 10 December 2019 (UTC)

Here is a direct link to the leaning towers. Richard Avery (talk) 08:54, 11 December 2019 (UTC)

Left and right in pictures

When describing a picture of two people facing the viewer, one can use "left" and "right" either from the viewer's perspective, or the perspective of the people in the picture. Somewhere, somewhen, I read that the decision which to use is affected by the culture one comes from, but I can't find a suitable reference for this online. Can anyone help? Henry^Flower 21:37, 10 December 2019 (UTC)

Have you read about § stage directions? Nimur (talk) 21:50, 10 December 2019 (UTC)

Interesting! Though annoyingly the perspectives mentioned there for English and Arabic speakers respectively seem the opposite of my experience with pictures (i.e. that English speakers use the viewer's perspective, and Arabic speakers that of the person in the picture). Henry^Flower 22:16, 10 December 2019 (UTC)

Another anomolous example is the technical art and practice of blazonry in heraldry, that is, of describing the elements of a 'coat of arms'. This, which uses a vocabulary based on 12–15th-century Anglo-Norman French, describes the arms as from the point of view of the putative wearer or carrier (in the case of the shield) who is facing the viewer, so that for example the dexter side of the shield is on the left as the viewer sees it, and the sinister side on the right. {The poster formerly known as 87.81.230.195} 2.217.209.178 (talk) 04:39, 11 December 2019 (UTC)

The example is as expected considering that the shield is there for the benefit of its carrier. It's as understandable as the need to cut costs on decals explains why the pony prances backwards on the right hand side of Ferrari cars. DroneB (talk) 11:12, 11 December 2019 (UTC)

The shield benefits the carrier, but the blazonry is there for the viewer - the bearer can't even see it (and, if they do, ta da! the left is now the right after all). Matt Deres (talk) 15:28, 12 December 2019 (UTC)