Science desk
< December 3	<< Nov \| December \| Jan >>	December 5 >

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.

December 4

What building collapses resembled the WTC towers collapses?

What kind of dynamic loads were the most responsible for bring them down? Thank you. 104.162.197.70 (talk) 01:37, 4 December 2019 (UTC)[reply]

The parts of the buildings above where the planes hit. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:25, 4 December 2019 (UTC)[reply]

The collapses were examples of progressive collapse; see that article for other instances. (Collapse of the World Trade Center could maybe use a little editorial work.) --47.146.63.87 (talk) 04:58, 4 December 2019 (UTC)[reply]

Not many. The WTC (also the Aon Center in Chicago and an IBM building in Seattle) are examples of Fazlur Rahman Khan's framed tube construction. These are efficient structures at providing large clear floor areas, because they concentrate much of their structural strength into the outside wall. This is a strong structure, but it also means that any large impact is also likely to damage more of it than a more traditional structure where the framing is distributed across the plan. Thus any collapse would be of a different nature. See Construction of the World Trade Center and Collapse of the World Trade Center. Fortunately no other such buildings have suffered an attack like that.

Even the Sears Tower, which uses a bundled framed tube structure, would have less such dependency on its outside layer. Andy Dingley (talk) 18:51, 4 December 2019 (UTC)[reply]

I'm not much of an expert on skyscraper architecture, but are you saying that the World Trade Center, unlike many other skyscrapers, used Load-bearing walls in a way that made them uniquely susceptible to the kind of collapse that occurred after the towers were struck by the planes? --Jayron 32 19:03, 4 December 2019 (UTC)[reply]

No, I said that the WTC (also the Aon Center in Chicago and an IBM building in Seattle) are examples of Fazlur Rahman Khan's framed tube construction. Andy Dingley (talk) 19:11, 4 December 2019 (UTC)[reply]

Yeah, I read that, but I was asking instead about your statement "they concentrate much of their structural strength into the outside wall". Is that what is meant by a load-bearing wall or is that something else entirely? I apologize that the source of my confusion wasn't clear. --Jayron 32 19:15, 4 December 2019 (UTC)[reply]

It's a framed tube. It's regarded as innovative. Now in some ontological sense, it's a wall and it's load-bearing. But you won't learn much from that article, you'd be better at the linked one. Load-bearing walls have been around nearly as long as walls, and this is unlike most others. Andy Dingley (talk) 19:19, 4 December 2019 (UTC)[reply]

Got it. Thanks for clarifying. --Jayron 32 19:20, 4 December 2019 (UTC)[reply]

Twins versus conjoined twins

Why do we often see twins of the opposite sex (i.e., a brother and a sister) ... but we never see conjoined twins of the opposite sex? Every time I see conjoined twins, they are of the same sex. Also, is there such a thing as conjoined triplets (or a higher number, besides twins)? My guess is "no" ... but, why not? Thanks. Joseph A. Spadaro (talk) 18:01, 4 December 2019 (UTC)[reply]

By the same reason that you will never see identical twins of the opposite sex. You can also see Twin#Degree_of_separation. As to identical triplets or conjoined triplets, they are also possible. Ruslik_Zero 18:40, 4 December 2019 (UTC)[reply]

Just to add a little more to Ruslik0's excellent response; the term twins actually refers only to two individuals who are gestated at the same time; but there are actually many different types of twins based on how there came to be two individuals in that womb together. Twin#Types and zygosity discusses all of these in some detail, but perhaps goes a bit too deep in the weeds. We usually think of twins coming in two main types, identical twins and fraternal twins, with identical twins being formed by a single zygote and fraternal twins being formed by two different zygotes. Fraternal twins are, except for being gestated at the same time, otherwise just like non-twin siblings. The share a 50% relationship in genetics, for example. Also, the chance of two fraternal twins being of the same or different biological genders are exactly the same for any other sibling pairs: 50% of them will be one of each, 25% of the time they will both be boys, and 25% of the time they will both be girls. Fraternal twins cannot be conjoined because at no point in their development were they ever the same individual. Identical twins, on the other hand begin as a single individual zygote that splits early in development into to identical, but separate, individual zygotes. Conjoined twins happen basically because this "splitting" process is incomplete. Because identical twins are genetically identical, they are always the same biological sex at birth. (as an aside, this does not preclude one of a set of identical twins from having a different gender at a later point in their life.) Because conjoined twins are always identical twins, and because identical twins are always the same biological sex as each other, conjoined twins are always of the same biological sex. --Jayron 32 18:54, 4 December 2019 (UTC)[reply]

Nitpick: the more standard terminology today (as used by bodies such as the WHO) is to use "sex" to refer to a person's sex chromosome genotype. See sex and gender distinction. --47.146.63.87 (talk) 20:02, 4 December 2019 (UTC)[reply]

Good point. Thank you for bringing that up. So corrected.--Jayron 32 23:08, 4 December 2019 (UTC)[reply]

Just because nature can do funky things, separate zygotes can fuse, meaning a fertilization event that would normally lead to fraternal twins can instead lead to a single chimeric offspring. And there are rare cases of sesquizygotic twins, where what starts as a single ovum is fertilized by two separate sperm, with the resulting [blastomere]] later separating into twins. Apparently there's an increased likelihood that the cells with the two different paternal generic lineages form separate clusters rather than being homogeneously mixed. If one of the two involved sperm were genetically X and the other Y and the two parts of the blastomere had different relative amounts of these lineages, they can lead to twins with different sexes. Doi:10.1056/NEJMoa1701313 and refs therein is an interesting read! "All it takes" is for the twinning event to be incomplete in this case, and you have conjoined twins of opposite sex. DMacks (talk) 05:03, 5 December 2019 (UTC)[reply]

Indeed, edge cases and oddities do exist, and thank you for bringing that up. "All it takes" is some actual examples; though. We can hypothesize all day, but of the billions of births in history, do we have examples of mixed-sex conjoined twins? --Jayron 32 12:20, 5 December 2019 (UTC)[reply]

No examples yet known for humans (and apparently armadillos are the only other placental species to have monozygotic twinning). There is one report of conjoined phenotypically different twins,(doi:10.1002/ccr3.2113) but not developmentally oppositely sexed. DMacks (talk) 15:08, 5 December 2019 (UTC)[reply]

Thanks! Makes sense. But, back to my question about conjoined triplets, etc. The example that an editor gave above was about three children (triplets), but only two of the three were conjoined. My original question was asking about all three triplets (or more) being conjoined. Does this happen? Why not? Thanks. Joseph A. Spadaro (talk) 04:29, 5 December 2019 (UTC)[reply]

[1]. Found on a first-page google search. --Jayron 32 12:20, 5 December 2019 (UTC)[reply]

The part unsaid is that there is a difference between what is possible and what is likely to survive to birth. Multiple births greater than twins are relatively rare in the first place, so you'd be multiplying one unlikely occurence against another unlikely occurence just to have conjoined triplet or quads develop at all. Combine that un-likelihood with the risks associated with multiple births and it's no wonder you don't hear about them being born. Matt Deres (talk) 14:30, 6 December 2019 (UTC)[reply]

@Matt Deres: Yes, excellent points! Exactly what I was thinking. Joseph A. Spadaro (talk) 04:50, 7 December 2019 (UTC)[reply]

Thanks, all. Joseph A. Spadaro (talk) 20:21, 8 December 2019 (UTC)[reply]

Best tree for carbon capture

Which is the best species of tree for carbon capture? Evergreen or deciduous? Broad-leaved or narrow-leaved? Larger or smaller? Or is it just the species that grows fastest, i.e. the first to reach maturity? Am not sure if any species have been named in the various election manifestos from the political parties currently published in the UK. Perhaps they would all just go for the cheapest one? 86.190.108.100 (talk) 18:59, 4 December 2019 (UTC)[reply]

There is a variety of sources here where you can research some of the answers for your question; I will note as an aside that I would think that the best kind of tree to plant would be the ones that are native to, and thus would grow best in, the particular area where you live, and thus there isn't a "one tree fits all" answer for every ecosystem in the world; the world already has a problem with monocultures and loss of biological diversity, and I would think that the proper response in terms of which plants to encourage to grow would be different (for some places, trees may not even be the correct response). But on the narrow nature of the original question, there's several sources in my link for them to choose from. --Jayron 32 19:09, 4 December 2019 (UTC)[reply]

Is the best carbon capturer even neccessarily a tree? Perhaps there are grass or even algae species that outperform trees. Roger (Dodger67) (talk) 19:14, 4 December 2019 (UTC)[reply]

This source gives some analysis of the promises - [2]: Tories 30 million a year, LibDems 60 million, Labour 60 million until 2025, then 140 million 2025-2030, and 100 million 2030-2040, Greens 70 million. But there's not much detail on types there. Labour says in its Plan for Native "We will plant mixed native woodlands". But I don't think the others don't give much detail. 86.190.108.100 (talk) 20:11, 4 December 2019 (UTC)[reply]

One thing that many politicians get wrong is that when a tree (or some algae or grass) captures some carbon, when it dies and either rots or is burned it releases all of that carbon right back into the atmosphere. What you really want to do is to grow something and them bury it, make furniture or houses out of it, create a new forest and keep the forest in place so that when trees die new trees replace them, or figure out some other way to keep the carbon from going back into the environment. --Guy Macon (talk) 20:35, 4 December 2019 (UTC)[reply]
While a tree may die and return its carbon to the atmosphere, a healthy, mature, permanent forest would become an essentially permanent store of carbon. Planting a tree in your front yard is not a permanent solution; allowing and encouraging fallow land to be reclaimed by the local ecosystem (which may be a forest) would. Increasing population density (building up rather than out) would. Etc. --Jayron 32 12:10, 5 December 2019 (UTC)[reply]

Maybe the homes of the future will be made of grass and algae? But that doesn't sound like such a vote-winner. Martinevans123 (talk) 20:47, 4 December 2019 (UTC)[reply]

Straw-bale construction is already a thing, with somewhat more success these days than the first little pig had. HiLo48 (talk) 04:08, 5 December 2019 (UTC)[reply]

For "carbon capture", the role of phytoplankton in the carbon cycle can't be beat -- but political parties can't get votes and greenies can't get taxpayer funding from them. 107.15.157.44 (talk) 04:56, 5 December 2019 (UTC)[reply]

AIUI plankton that manages to avoid being eaten eventually becomes sludge on the sea floor. (Some of) this sludge in turn becomes petroleum after spending some millenia in a geological pressure cooker. Roger (Dodger67) (talk) 08:34, 5 December 2019 (UTC)[reply]

Tangent Alert:

Whereas trees often vote for their favorites. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:12, 5 December 2019 (UTC)[reply]

...Thus explaining the Green party. --Guy Macon (talk) 06:15, 5 December 2019 (UTC)[reply]

Some trees seem decidedly opposed to elections at all.[3] DMacks (talk) 06:27, 5 December 2019 (UTC)[reply]

The headline "Tree falls on polling site, still able to vote" suggests that although the tree fell, it was still able to cast a vote. A feel-good story! ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:42, 5 December 2019 (UTC)[reply]

Some trees try to get elected to Congress: [4] 107.15.157.44 (talk) 06:46, 5 December 2019 (UTC)[reply]

Some have been: Fernando Wood William B. Pine. And going the other way, The Senator (tree). DMacks (talk) 07:05, 5 December 2019 (UTC)[reply]

Back to the point: “With increased species richness, more carbon is stored both above and below ground – in trunks, roots, deadwood, mould and soil. You can roughly say that a diverse forest stores twice the amount of carbon as the average monoculture.” From Forests containing several tree species could store twice as much carbon as the average monoculture plantation, research finds. Alansplodge (talk) 17:44, 5 December 2019 (UTC)[reply]

And from a UK perspective: Trees as carbon stores lists species with high, medium and low carbon sequestration rates. Only three in the "high" category are native to Britain, so I suspect that the Labour Party's emphasis on native species is more to do with improving wildlife habitat than with carbon capture. One of the trees listed as "high" is the dreadful Leyland cypress, a forest of these things would be a wildlife desert. Alansplodge (talk) 17:50, 5 December 2019 (UTC)[reply]