Wikipedia:Reference desk/Archives/Science/2020 October 6

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October 6

Iron silicides

What is the oxidation state of iron in iron monosilicide (FeSi)? Its placement in Template:Iron compounds under iron(VI) looks wrong, since silicon can't have a -6 oxidation state. I'll ask the same question about the other iron silicides (FeSi₂ and Fe₂Si) and FeGe. –LaundryPizza03 (dc̄) 03:08, 6 October 2020 (UTC)

• For FeSi you could say formally IV, but the silicon atoms appear to have bonds between them, so it might be more like Si₄^8- with 4Fe²⁺. For the disilicide it looks more like a formal VIII, but that is getting a bit extreme, and there would be even more Si-Si bonding, so it would be better to say that Si is not 4- and is instead more like Si₄^4–. In practice you could use X-rays to get a better idea of oxidation number - ie how many electrons are on the iron. Graeme Bartlett (talk) 06:15, 6 October 2020 (UTC)

But do you have any sources about this? Can I assume they are all Fe(II)? –LaundryPizza03 (dc̄) 17:17, 6 October 2020 (UTC)

A source for the disilicide XANES is Statistically meaningful data on the chemical state of iron precipitates in processed multicrystalline silicon using synchrotron-based X-ray absorption spectroscopy Fig 2. But you have to interpret the highest slope of the pre-edge to get an idea of the oxidation state. There does not seem to be much research in this area, and there looks to be more studies of minerals, where iron is either 2+ or 3+. Graeme Bartlett (talk) 00:04, 7 October 2020 (UTC)

"Average electrons in the d orbitals are found as  ~6.5" according to this paper, so it's Fe^1.5+ on average. Pelirojopajaro (talk) 11:34, 7 October 2020 (UTC)

Sir Herbert Macauly

Moved to Wikipedia:Reference desk/Humanities#Herbert Macaulay - moved from Science Desk. DuncanHill (talk) 18:48, 6 October 2020 (UTC)

Depth Perception in certain birds

We've all observed how birds such as doves and chickens move their heads in a jerky manner as they walk. It's my impression that this action might be a means of creating a stereoscopic vision of their surroundings, by comparing successive visual images 'snapped' when the head is momentarily stationary at each step. These birds have very limited conventional stereo vision, in that only the area immediately in front of their beaks falls within the visual coverage of both eyes. A way of monitoring their surroundings in this way would be a useful survival instinct. I'm not a biologist (I had an engineering background during my working life), so this is perhaps a well-known field which has been covered at length by experts. Could you perhaps tell me if my surmise is correct? — Preceding unsigned comment added by Robert H Walton (talk • contribs) 14:42, 6 October 2020 (UTC)

Our article on Bird vision suggests that (some) birds move their heads in order to detect the Earth's magnetic field. Whether that's relevant to chickens, I would doubt but it seems reasonable for doves. Michael D. Turnbull (talk) 16:30, 6 October 2020 (UTC)

These articles[1] [2] [3] suggest the reason (for pigeons) is to allow the birds to hold their heads still for short periods while they walk, to allow their visual system to process the images they see. When birds walk in an environment where their view of the world doesn't change as they walk (eg. on a treadmill), they don't bob their heads. It's not related to steoscopic vision per se, just to allow an image to stabilize on each eye. Humans do it less conspicuously by moving their eyeballs instead of their whole heads. CodeTalker (talk) 17:54, 6 October 2020 (UTC)

To elaborate on this, when humans are taking in a scene, their eyes alternate between being briefly stationary, fixating on a point in the scene, and quick movements, called saccades, to a next point to focus on. The visual system processes what is received during the stationary moments; transmission from the retina to the visual field in the cortex is suppressed during a saccade, so we are then in a sense functionally blind during that period – for only a fraction of a second at a time. Saccadic eye movements are coordinated with head movements in walking chickens.  --Lambiam 21:52, 6 October 2020 (UTC)

Microsaccades, for I have become saccade of saccades, destroyer of stationarity. Sagittarian Milky Way (talk) 22:06, 6 October 2020 (UTC)

The explanation I read long time ago: These birds' eyes don't see anything when they don't move because they are optimized for the perception of external movements. So if the bird wants to see its environment it must move its head and as a result birds will alternate short periods of head immobility during which time they could reliably discover an approachingt predator with short periods of head movements during which time their eyes can see the grains on the ground. 2003:F5:6F09:7A00:5C6F:45E4:48E:19B3 (talk) 16:09, 7 October 2020 (UTC) Marco PB

References

Peristalsis in dinosaurs and various birds

I understand that present-day birds evolved from dinosaurs. When we contemplate huge dinosaurs such as hadrosaurs, with small heads and metres-long necks, it would seem that they would need an efficient system of peristalsis to be able to ingest enough food to survive. This facility presumably carried over to birds in the process of evolution, but we see that some modern birds have it and some don't. For example, doves and pigeons dip in their beaks and gulp down water, but chickens and most garden birds (the ones I have observed, anyway), have to take a beakful then extend their necks to let the water trickle down. Given that the theory of dinosaur-to-bird evolution is fairly recent, can I ask whether any work has been done on the carry-over of peristalsis to birds? One assumes that proto-birds were bird-sized dinosaurs which might not have had peristalsis, but then is it likely that doves, etc, would have re-evolved it? — Preceding unsigned comment added by Robert H Walton (talk • contribs) 18:32, 6 October 2020 (UTC)

Most dinosaurs are not huge. Probably ancestors of birds were not huge either. Graeme Bartlett (talk) 23:11, 6 October 2020 (UTC)

"Swallowing is accomplished by esophageal peristalsis, and in most birds appears to be aided by extension of the neck". Colorado State Univesity - Digestive Anatomy and Physiology of Birds

Hadrosaurs didn't have particularly long necks compared to their heads (nor particularly small heads compared to their bodies). They are also ornithischians ("bird-hipped dinosaurs"), whereas birds, ironically, evolved from the saurischians ("lizard-hipped dinosaurs"). More specifically, they evolved from small therapods, similar to Velociraptor. "Small heads and metres-long necks" sounds like you mean the sauropods (Brontosaurus and the like), which are also saurischians, but not that closely related to the group that birds came from. Iapetus (talk) 08:56, 7 October 2020 (UTC)

" Given that the theory of dinosaur-to-bird evolution is fairly recent" Not really. Thomas Henry Huxley proposed the idea in the 1860s (about as early as it could possibly be done). It has enjoyed varying levels of support over the years since. --Khajidha (talk) 11:14, 7 October 2020 (UTC)

It seems to me that all birds possess some esophageal peristalsis because even birds that extend their necks when drinking don't need to do so in order to swallow grains or whatever. So it is well possible that all birds can swallow water without extending their necks but that some of them discovered that they can drink more water more quickly than the competitors if they additionally extended their necks.

On the other hand if a character has no clear advantage it can easily become lost in 50 or 90 million years. So if you don't have sources stating that 1) some birds don't possess peristalsis and 2) not possessing peristalsis is a serious disadvantage for them, then your question is objectless. 2003:F5:6F09:7A00:5C6F:45E4:48E:19B3 (talk) 16:17, 7 October 2020 (UTC) Marco PB

BIOLOGY - Latin binomial nomenclature, e.g. Iris variegata vs. Iris variegatus

Hi there! Could somebody explainify what the deal is with latin names sometimes ending in -a and sometimes in -us. Older names perhaps? Plural? Is one of these names more preferable or even the only correct form? Thank thee kindly. Life is so... confusing. --Palosirkka (talk) 22:40, 6 October 2020 (UTC)

Take a read of Binomial nomenclature#Derivation of binomial names. They have to agree in grammatical gender. The -a will be feminine, and the -us will be masculine, and so will not be interchangeable on the same genus. Graeme Bartlett (talk) 23:10, 6 October 2020 (UTC)

Right. So I guess Iris variegata is correct since Iris is feminine in latin and the other form is just wrong. Thank you. --Palosirkka (talk) 00:22, 7 October 2020 (UTC)

I can confirm that Iris is feminine in Latin, in my dictionary. Get a clue from link colour for Iris variegata, Iris variegatus and Iris variegatum. Graeme Bartlett (talk) 02:29, 7 October 2020 (UTC)

It may be added that other endings are possible; for example, the Canada goose is Branta canadensis. See Latin declension for more than you probably want to know. --174.89.48.182 (talk) 06:38, 7 October 2020 (UTC)

Yes, the link given above (Derivation of binomial names) explains it very well, but, for those that don't click through, what is missing from the discussion here is that the agreement in gender is only necessary if the species (i.e. second) name is an adjective. It can also be a noun in apposition or a noun in the genitive case, in which cases there is no agreement in gender. It is not always easy to be sure which of these cases apply, although modern species descriptions that coin new names should specify this if there is any possibility of ambiguity. Jmchutchinson (talk) 18:22, 7 October 2020 (UTC)