Wikipedia:Reference desk/Archives/Science/2018 September 27

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September 27

Plutonium density

According to the article allotropes of plutonium, the least dense phase is the δ phase, and it has a face centered-cubic structure. But a fcc structure is one of the two most dense packings possible, the other being hexagonal close-packing. How is it that the most dense packing structure gives the least dense allotrope? 202.155.85.18 (talk) 06:39, 27 September 2018 (UTC)

• The article matches the refs, even though it seems extraordinary. (A negative thermal expansion coefficient for a crystal? Come on...) Ref #2 lists (p. 294) your remark as "unusual property" #5 and ascribes it to nonstandard behavior of the 5f electrons (p.296 and following give an explanation but I find it hard to follow); in other terms, the "rigid spheres with a constant atomic radius" model is too wrong to apply it here. Tigraan^{Click here to contact me} 07:18, 27 September 2018 (UTC)

Hmmmm...actually that makes a lot of sense. The Goldschmidt correction for actinide series elements is probably much larger due to the lanthanide contraction, so as the coordination number is increased going to more and more close packed structures, the metallic radius increase is so great it leads to overall lower densities. Thanks! 202.155.85.18 (talk) 07:26, 27 September 2018 (UTC)

I don't know what the bloody hell you two are on about but that was great. It almost made me want to follow the links. (I always found physical chemistry banal). — Preceding unsigned comment added by Greglocock (talk • contribs) 09:56, 27 September 2018 (UTC)

Exoworlds with glowing vegetation

I believe that exoworlds with colorful glowing plants covering much of the world exist like Pandora from Avatar. What do you guys think? Glowing plants are obviously very uncommon on Earth with the most common species being sea-dwelling kelp. PlanetStar 21:11, 27 September 2018 (UTC)

See article Bioluminescence for the glowing and its functions. Contrary to your assumption the Abyssal plains (depths below 3,000m) actually cover more than 50% of the Earth’s surface! Since there is hardly any sunlight reaching these deeps - even the Macropinna microstoma, that uses giant eyes pointing upwards to detect prey against the light from the surface, prefers much higher zones around 1000m depth - and Bioluminescence is pretty common in these deeps, we actually have masses of glowing lifeforms here at "home". Just no "jungles" full of it because all food sources are way to scars that deep, to feed so much life.

One interesting revelation, since you cite the Movie Avatar as reference, is that the Director of that movie, James Cameron, actually became an expert on deep-sea exploration and thus certainly saw lots of Bioluminescence down there himself, which probably inspired him to add this to his computer generated jungle world Pandora and its biosphere. --Kharon (talk) 22:12, 27 September 2018 (UTC)

James Cameron seeing bioluminescent lifeforms deep below the ocean's surface inspired him to generate jungle of bioluminescent plants, both on land and underwater in the Avatar movie, which in turn inspired me to ask question about the real life existance of such a jungle on alien worlds by watching it. Although bioluminescent plants and animals are abundant deep in the ocean, why is bioluminescence so uncommon on land plants and animals? Isn't Earth unusual for a life-bearing planet to not have land bioluminescence in abundance? PlanetStar 21:18, 28 September 2018 (UTC)

In most cases bioluminescence is rather faint. There are some "surface" plants like Schistostega pennata where bioluminescence seems to have a benefit but our earth vegetation actually thrives great without it. Avatar is just a fantasy movie. You certainly will not find flying mountains anywhere in our universe for example. But they look spectacular of course - like bioluminescent jungles or elegant 3.5 meters high blue-coloured humanoids with huge shiny eyes do. Again, it's a movie. Don't read too much into it, especially when it's from the Sci-fi or fantasy genre. --Kharon (talk) 12:28, 29 September 2018 (UTC)

Isn't Earth unusual for a life-bearing planet to not have land bioluminescence in abundance? How could we know, since we've not discovered life anywhere else yet? —PaleoNeonate – 19:37, 30 September 2018 (UTC)

Fireflies put on an impressive display, but a fairly dim one; nature can be stingy. (pure speculation:) Still, I'm thinking that the abyssal plain is always dark, but the Earth, even at night, is often moonlit. Perhaps a planet without a moon would encourage more investment in bioluminescence? Another issue for plants is that their potential mates can neither see the display nor respond to it; they could signal to pollinators but other methods might be cheaper. But, what if another planet developed somewhat mobile plants with some degree of color vision? In truth, of course, we know nothing at all about other biospheres, nor can we predict them with any confidence. Wnt (talk) 00:38, 30 September 2018 (UTC)

I know Pandoran jungles seem fantastical, well, who knows, alien biospheres can be fantastical too. From my point of view, why isn't the Earth covered in Pandora-like glowing jungles and forests on land, while from Cameron's POV why isn't plants glowing deep underwater cover much of the land too? Maybe it's just the way the Earth's evolution went. My sister said had evolution gone in a slightly different direction, we would possibly see land forests/jungles of glowing plants. Of course it's far more likely to see these than flying mountains. Sci-fi never even look into rocks that fly, at least from my point of thought. PlanetStar 03:02, 30 September 2018 (UTC)

If you think rocks don't fly, watch a volcanic eruption sometime. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:23, 30 September 2018 (UTC)

Uuuuhhh, that's right! I could now say rocks don't have feathery wings and aren't self-aware. PlanetStar 19:29, 30 September 2018 (UTC)

Gecko in or out of house?

Background: I live in a large house in Algeria, where daily outside temperatures are typically from ~ 17 to ~ 27 C. There are cats in one room of the house (don't ask). The population of flies in the house seems fairly minimal to me. I see adult geckos outside the house, and occasionally find baby ones inside (not in the room which has cats, but they could get under the door). I typically transfer the babies outside, in the basis that they're more likely to live long and happy lives there.

My question: am I right, or am I just providing food for various predators? I realise refdeskers can't calculate the odds of a particular gecko being stood on / eaten by cats / freezing to death, but in general terms, is there a scientific basis for thinking they're better off in or out? 105.235.137.66 (talk) 21:12, 27 September 2018 (UTC)

It's typically 17-27 but they might freeze to death? I assume this is not the low desert? Sagittarian Milky Way (talk) 00:11, 28 September 2018 (UTC)

How does one freeze at 17C?--Jayron32 00:30, 28 September 2018 (UTC)

OP says "Daily outside temperatures are typically from ~ 17 to ~ 27 C".

Our article says "on the steppes of the High Plateaus winter temperatures hover only a few degrees above freezing". Rojomoke (talk) 04:46, 28 September 2018 (UTC)

The IP geolocates to Algiers, which has Csa sub-climate classification. Regarding the original question, it is essentially a matter of opinion, which this reference desk doesn't provide (stop laughing!). That being said, I'd be inclined to let nature take its course; if the geckos manage to find enough bugs to eat in your house -- great! Otherwise, they just might leave the way they came in (or end up being a nutritious cat snack). In many places it is considered good luck to have a gecko in the house (Hawaii, Indonesia, etc.). —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 06:00, 28 September 2018 (UTC)

Thanks, 2606, for not completely ignoring the question. Re: temperatures, I should have specified currently (could also have specified that dying of cold does not necessarily require temperatures literally below freezing). Re: opinion, I was hoping for (e.g.) some animal welfare society guidelines, which would be based on expert knowledge. All I find online is about caring for captive gecks. 105.235.137.247 (talk) 07:09, 28 September 2018 (UTC)

I never heard of "geckos" before. I only came across the word in a description of a browser using Chrome/Internet Explorer where it says "like gecko". What does that mean? 86.131.233.235 (talk) 09:39, 28 September 2018 (UTC)

See Gecko. Or watch some Geico TV commercials. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:08, 28 September 2018 (UTC)

While it's possible that your decision to take a pro-active vs. laissez-faire approach may have a massive impact on any one gecko (one may, as you fear, be snatched up by a predator instantly), as a probabilistic matter it is unlikely that your habit of removing them has a substantial net effect one way or another (that is, if you remove a hundred of them in a given year, probably close to the same number will meet their end shortly after their encounter with you). Young geckos, like most juvenile lizards, have a higher ounce-to-ounce metabolism than adults as they develop and specimens of almost all species likely to be in your house utilize a lot of energy in movement. Consequently, those individuals from species which have not developed a mechanism for storing energy in fat reserves (there are numerous of these, such as the fat-tailed gecko and the leopard gecko) need to eat fairly consistently, and they rely very much upon the conditions of their ecological niche for predation. This means that most geckos who end up in your house, particularly the young ones, will quickly begin to feel the pangs of hunger. That said, while there may be the occasional home which has features that make it likely to confuse a gecko guest such that they become trapped, by and large they will not have much difficulty in finding their way out again when circumstances prompt them to--so provided there are no environmental hazards inside the house (of the feline variety or otherwise), they should be fine if you leave them be.

Of course, this all assumes that the effort you are going to exert is limited to walking them to the door. If you really want to give the best possible chances to your reptilian boarders, you should identify the exact species, learn which flora provide them the best hunting and defense opportunities and deliver them to the nearest acceptable specimen. Most adult geckos will also be more than happy to accept mealworms or crickets, if you can find a supplier that provides them and have the patience to set the gecko up in a vivarium for a while--if you were really dedicated to giving them a leg up on their way out the door. Sorry I can't find a suitable source for all of this; I did look but couldn't find anything particularly on point--this is just a summary of various details I happen to know regarding lizard physiology and ethology. Snow ^{let's rap} 09:45, 28 September 2018 (UTC)

Thanks, that's useful. To clarify, when you say if you remove a hundred of them in a given year, probably close to the same number will meet their end shortly after their encounter with you, do you mean just that most baby geckos don't survive long, or the ones I find are most likely already in bad shape? I'll try to identify the next one, in case I can do better by him. 105.235.137.247 (talk) 10:38, 28 September 2018 (UTC)

Well, survival rates will vary by species and location, but what I meant is that over a large enough sample size, your decision to remove them or not remove probably will not have a significant impact on the longevity of the Gecko's in that particular group, collectively. That is, you will probably not have a big impact on their fortunes (on average) whichever approach you land on (again, assuming you are just taking the ones you remove to the door).

Incidentally, there is another consideration I didn't think to mention before that I'll emphasize now; as a cat owner, you may wish to remove the geckos just to reduce the likelihood that they may come into contact with your feline roomates; lizards oftentimes carry parasites, some of which your kitties could possibly contract from ingestion. Small mammals are more likely to operate as this sort of vector than reptiles, but better safe than sorry. It's also a really bad way to go for the lizard; domestic cats typically do not hunt out of hunger, if they are owned and properly fed, so they drag the affair out to excruciating length before eating just bits. As someone who has done some wildlife rehabilitation, I can tell you that there's little that's more difficult to deal with than an animal a cat had a hold of for half an hour--but refused to finish off, because it was entertained by the movement. Geckos probably go a bit faster from abdominal puncture wounds, because of their size relative to a cat, but still, a miserable end. And sure, no problem--happy to help. :) If you need assistance in identifying the species, let us know, and feel free to ping me. Snow ^{let's rap} 10:54, 28 September 2018 (UTC)

Good points. The cats are completely inept hunters, which would probably prolong things even if they didn't want to. As long as I'm not clearly sending the little guys to their deaths, I think I'll continue with my transfer policy, while trying to find an optimal drop-off point. 105.235.137.247 (talk) 15:26, 28 September 2018 (UTC)

If you've got little geckos slithering their way into your house, what other, smaller creatures might be invading also? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:02, 28 September 2018 (UTC)

I think that carrying capacity is the relevant concept here. It is very difficult to predict, short term, the effect of releasing a few extra geckos into a wild population. They might, after all, be momentarily low in numbers for some reason, so that the introduction of new blood helps them to recover faster. Or, they might be near a population crash where a few extra mouths help them all to starve. But if you come back in fifty or a hundred years, the number of geckos each year will follow some random pattern that will depend in no significant way at all on how many you released. What this means is that for every gecko you lovingly feed, nurture, and defend as it makes its way into the wild, there is another gecko which is pushed aside by your newcomer and crawls off to some unwatched corner of the wild to die.

The situation in your house may be the same; in that you may be relatively inefficient at catching geckos so that the "predation" imposed by your good intentions (plus the doorway to the room full of cats) actually has little real influence on the total population. Much likea properly managed hunting or fishing season in the wild would be. On the other hand, you certainly could catch every single last gecko and put up a Great Wall of Trump to keep out any future invaders, and leave the stray bits of kitty kibble to be dealt with solely by some other member of the ecosystem (bacteria, mold, cockroaches, or Roomba). Then, there would genuinely be some lost gecko-hours of home enjoyment lost forever to history.

I think the reason why this seems surprising to our expectations is that with humans there is a culture. We expect that if there are more people, eventually they discover plows, domesticate plants and animals, or do genetic engineering trying to improve the carrying capacity of the environment, also they may actually limit their own fecundity, all of which means that increasing their numbers now doesn't automatically guarantee exterminating the same number in the future. (Though it scarcely rules it out either) Wnt (talk) 19:39, 28 September 2018 (UTC)

Interesting! In this particular case, geckos here suffer from religious persecution (not every day you get to write that), so perhaps carrying capacity is not the limiting factor. 105.235.137.251 (talk) 22:27, 28 September 2018 (UTC)

I couldn't help but take that bait: [1][2][3][4][5]. I didn't come to any strong conclusions, but it's interesting. Wnt (talk) 23:27, 28 September 2018 (UTC)

Mainly this. There may be a pragmatic origin related to e.g. parasites, but basically it's superstition. 105.235.137.251 (talk) 06:17, 29 September 2018 (UTC)

What I was referring to was this sentence in my browser configuration details:

AppleWebKit/537.36/KHTML, like Gecko

I googled the term but there is nothing listed. What does it all mean? 86.131.233.235 (talk) 17:34, 29 September 2018 (UTC)

Gecko (software) is the "browser engine" that displays a document in the web browser, after it has somehow been obtained. It explains at the first article how Apple made its own version in 2001, back when Netscape was a popular browser, but one that took a long time to start up on account of all the "software bloat" it had accumulated. Wnt (talk) 18:26, 29 September 2018 (UTC)

Now I understand why they call it a "search engine". I had always wondered. Thanks. 86.131.233.235 (talk) 18:53, 29 September 2018 (UTC)