Wikipedia:Reference desk/Archives/Science/2020 August 15

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August 15

Would 1368x208x208 of solid wood sway more than a skyscraper? Or collapse easier?

Dimensions are the aboveground portion in feet, belowground part is let's say 208x208x208 feet with half in soil and half in strong bedrock but just a tight fit mating, not glued, piledriven or otherwise attached. Wood type, grain direction, part of tree, lumber dimensions is strongest possible, skyscraper is Manhattan code, not supertyphoon and strong earthquake resistant like Taipei. Does it depend if fastening is skillful nailing, skillful screwing, skillful gluing (thin layer only) or skillful piece interlocking (like pagodas, no fasteners whatsoever)? Can it have a stairway big enough for a man to reach the roof or even some rooms too and still be strong enough? It would of course remain a useless fire risk that might rot unless exposed faces are sealed. Sagittarian Milky Way (talk) 02:36, 15 August 2020 (UTC)

This question sounds vaguely familiar. In any case, we have List of tallest wooden buildings, and it's possible you could branch out from there to find more info. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:09, 15 August 2020 (UTC)

The strength of solid wood in compression seems to be a few tens of megapascals, which for a density of 1, should support a few hundred meters.. There are trees around 100 meters high too. Anyway with your 400 meter building you are close to the limit for many kinds of wood, where it would fail under load. The stiffness of wood is about 8 to 12 gigapascals, if you can workout how that would sway, but I would expect a solid bar of wood like you suggest would be stiff. I guess that you could build a stairwell space inside and even rooms without them collapsing. if you glued many laminates to make a 208 foot thick plywood, that would do the job! to see what happene if wood is over loaded see https://www.youtube.com/watch?v=deWKSD6KBzQ Graeme Bartlett (talk) 06:01, 15 August 2020 (UTC)

On first reading I thought you (SGM) meant a solid wooden block of some 60 million cubic feet, which would sequester a lot of carbon. But I assume you envisage an assembly of wooden trusses. The rather unpredictable effects of spontaneous wood warping, at this scale, might cause a wooden structure to deform sufficiently to cause rupture of elements due to various stresses, such as the bending moment caused by gravitational forces due to asymmetric bending, even without the effects of wind or quakes. The dimensions of the structure are almost equal to those of One World Trade Center. It should be able to accommodate plenty of spacious boardrooms while leaving enough space for umpteen wide stairways. Does the floor plan have to be square, or can it be circular? The latter should be a lot easier to calculate through. (Not that I'm going to attempt this; too much depends on the specifics of the design for a back-of-the-envelope calculation.)  --Lambiam 06:18, 15 August 2020 (UTC)

So no hollow space is more likely to work. Would a 2496 by 2496 (like a 2 by 4 but bigger) 1576 feet long work if it could exist? I'm not sure what's the most fair way to extrapolate a width and height that cannot exist for a non-fungible substance with a concentric tube grain. Presumably megapascals would decrease with size from the nanoscopic defects in all materials. Sagittarian Milky Way (talk) 23:49, 15 August 2020 (UTC)

Gravity and fatigue

I'm aware of the known issue of muscular deterioration in space, requiring regular physical exercises. But, on the other hand, would humans experience less fatigue in a low-gravity environment (roughly comparable to that on Mars or Moon), particularly due to less strain on muscles (such as when standing) and due to less muscular effort required for many movements and tasks? Thanks. 212.180.235.46 (talk) 17:55, 15 August 2020 (UTC)

Immersion in shallow water, reaching to say the neck of the patient, has been used for revalidation therapy of injuries of the locomotion system, such as sprained ankles and ruptured muscles. By Archimedes' principle, the immersion results in a considerable loss of weight (not of mass), putting less strain on muscles, joints, etcetera and thereby facilitating certain exercises. The point is not to reduce fatigue and I don't know if anyone has studied this. Wading through water, in spite of the reduced weight, takes more effort for the same distance than walking on flat terrain. Walking on the Moon (at about one sixth of Earth's gravity) and on Mars (at about three eighths of Earth's gravity) should be easier than wading through water but will still require the walker to adjuat their gait, especially on the Moon. People who actually walked on the Moon reported no difficulty in moving around, though.^[1] Walking on flat Earth terrain does not require one's muscles to work "against" gravity like they need to do when walking up a ramp; so in that respect the reduction in effort is not large. To travel a larger distance it may be easier to hop or jump-run than to walk "normally" (Earth-style). This may require a similar energy per unit of time, but less for the same distance bridged. In the end it may depend on the specifics of the activities. Push-ups will definitely be easier.  --Lambiam 19:15, 15 August 2020 (UTC)

A quick Google revealed that fatigue in space is a big issue because of the difficulty of getting sufficient sleep. [2] Alansplodge (talk) 13:43, 16 August 2020 (UTC)

Is moving while in water a good comparison with moving in a low-gravity environment? I would have thought the physical effects are quite different, despite the reduced weight similarity - for a start, someone moving through water is working against a medium of much greater density than air, so I would expect the effects on muscles to not be wholly comparable. PaleCloudedWhite (talk) 14:27, 16 August 2020 (UTC)

Above I wrote: "Wading through water, in spite of the reduced weight, takes more effort for the same distance than walking on flat terrain." This indeed establishes that when it comes to moving "from A to B" immersion in water is not a good model for walking in a low-gravity environment? But what about fatigue reduction "due to less strain on muscles (such as when standing)", which was part of the question?  --Lambiam 17:24, 16 August 2020 (UTC)

Wading through water is hard because you have to displace a large mass of water. Because the wannabe astronaut is moving (water) sideways, gravitational force plays no role here, but inertial mass does. This seems to be an unsurmountable problem, because any medium dense enough that humans float in it, is by consequence massive. 93.136.48.85 (talk) 03:28, 17 August 2020 (UTC)

[Edit Conflict] Unfortunately, there are no good comparisons available, as simulating a lower gravity environment within a higher one is extremely difficult. Water immersion has proved a useful preparation for zero-g working because the water resistence somewhat mimics the effects of wearing an inflated spacesuit in a vacuum.

For low- (but not zero-) g conditions, elaborate systems of suspending people on carefully calibrated springs and harnesses from an overhead freely-moving framework have been tried by the Mars Society and others with questionable success (for one thing, they cannot mimic the effects of lower gravity within the body), and a modified parabolic flight path on the "Vomit Comet" to yield a low- rather than zero-g environment must surely have been tried, but would be limited both spacially and temporally.

Unfortunately the Mars Gravity Biosatellite program has been discontinued. Artificial gravity may include some further pointers. {The poster formerly known as 87.81.230.195} 2.122.61.94 (talk) 17:43, 16 August 2020 (UTC)

Chemical Sensors: New fields of study and application

Hi I have seen the description of the said topic but I wanted to get updated with latest advancements in this field of study, the field of chemical sensors is large I wanted to know about those sensors which detect chemical compounds or elements in traces and thir cost dependence i.e. which type are most costly. thank you.

regards. — Preceding unsigned comment added by 120.57.38.139 (talk) 18:28, 15 August 2020 (UTC)

I assume you have read the section Chemical sensor of our article Sensor. A freely available source is the e-book version of Progresses in Chemical Sensor, and another (non-free, somewhat older) text is Chemical Sensors and Biosensors: Fundamentals and Applications. The journal Chemical Reviews had a special issue last year devoted to the topic. (Accessing the contents requires an institutional login.) This Google Scholar search will produce references to recent scholarly contributions to the field.

As to the issue of cost, that is not something that can be answered in general terms. If depends crucially on the specific chemical or family of chemicals that needs to be detected as well as the desired detection threshold.  --Lambiam 20:37, 15 August 2020 (UTC)

Is a more space-efficient genetic molecule possible and/or a less convoluted genetic molecule to diverse amino acid-strings system..

..that still allows easy copying and turning sperm and ova genetic molecules into an alloy molecule with half info from each and a human-like mutation rate? Too rare a mutation is suboptimal too right? Can we skip some steps with better molecules? Why can't we have a ribosome-like organelle that can work on copies of the genetic molecule directly? (besides RNA genomes only working at tiny mutation reduction-friendly scales and Earth abiogenesis only happening once so we have to use whatever worked first whether optimal or not, and that it also has to bootstrap itself from primordial soup while it is not implausible that the optional genetic molecule requires an intelligent designer who doesn't seem to exist to make the first cell)

And is an organic genetic molecule possible that can store a human genome of information in less volume and still allow easy copying, reproductive gene shuffling, a human-like mutation rate and a not more convoluted way to turn genes into unattached strings of at least 20 amino acid types? Some kind of polymer or double helix with physically smaller phonemes perhaps, or a nucleic acid system with 6 or 22+ base types and 33 or 67 percent less bases. Could such systems even be chemically possible? I don't care much whether a better system can evolve from primordial soup by itself (no one could know probably), I'm just wondering if it would work. Sagittarian Milky Way (talk) 23:11, 15 August 2020 (UTC)

Synthetic biology investigates such questions on xeno-nucleic acids and related alternatives. Google Scholar indicates that there are thousands of papers on the subject. You may also look at viroids who may be "fossils" of an ancient acellular biotope. Hypothetical types of biochemistry may provide some useful references. --194.166.102.61 (talk) 05:54, 16 August 2020 (UTC) Oops, forgot to log in. --Cookatoo.ergo.ZooM (talk) 05:55, 16 August 2020 (UTC)

By the way why do you think that a more space efficient genetic molecule should be / have been an advantage? Or messenger-DNA instead of messenger-RNA? And what if ribosomes could operate directly on genes without the copying step? Would this not be an advantage? Or maybe not? A more 'space efficient' code would also possess less redundancy, thus probably allowing less efficient error correction, for example.

We can think that no other system has existed and competed with our DNA/RNA/20 aminoacids system, but we don't know. Maybe thousands of different systems have existed and only the really best-of-the-best one has survived. 2003:F5:6F0C:E600:4528:4457:E96E:9CF (talk) 10:00, 16 August 2020 (UTC) Marco PB

Wouldn't 6 base types and maybe smaller phonemes (not A, C, G, T or U) and/or thinner molecule spines still allow repeats for redundancy and be able to curl into a smaller chromosome? It may not be better but it'd be aesthetic. Sagittarian Milky Way (talk) 14:33, 16 August 2020 (UTC)

More code letters would request for a more complex and error prone t-RNA system, beside that redundance doesn't reside in repetition alone. Maybe molecular machines that process DNA such as helicases, recombinases and polymerases cannot be much smaller and still function resp. they could not process smaller NAs. And first of all, why do you think that smaller chromosomes should be a bonus? As far as I know only some viruses with huge genomes have any problem getting it into the capsid, but most nuclei are small in comparison with the cells that host them but large in comparison with the genome they support. 2003:F5:6F0C:E600:4528:4457:E96E:9CF (talk) 15:08, 16 August 2020 (UTC) Marco PB

So the current system might be pretty good after all. Sagittarian Milky Way (talk) 15:14, 16 August 2020 (UTC)

See Base pair#Unnatural base pair (UBP), which I found via a link from Synthetic genomics. DMacks (talk) 15:18, 16 August 2020 (UTC)

"Or messenger-DNA instead of messenger-RNA? " Messenger-DNA would probably be too stable to be useful. Remember, mRNA is read and disassembled quickly. It's basically a genetic post-it note. The structure of DNA is more durable than that of RNA. Making mDNA would be like leaving a note for your husband saying "buy milk" on high quality parchment.--Khajidha (talk) 12:16, 17 August 2020 (UTC)

Is tDNA possible? But too parchment-like probably. Sagittarian Milky Way (talk) 17:27, 17 August 2020 (UTC)

I think we are mixing here two very different questions: 1) are such fantasy biochemistries possible? Yes, why not? A genome out of marshmallow would code information just as well and instead of aminoacids some completely different molecules could also build up suitable structural bricks and catalysts. But 2) would such alternatives give some advantage to the life form using them? Here I dare to be skeptical. On one side it is true that every time one particular solution has taken a foothold, other solutions maybe just as good or even better don't find any more room to develop. But on the other side: 3.5 billions years and 1 billion cubic kilometers of water that is an awful lot of time and place for experiments, and I do believe that if for example DNA would give a messenger just as good as mRNA, then at least some form of life would exist that use mDNA.

So I do repeat my question to Sagittarian above: in your opinion, what kind of advantage would smaller chromosomes or different aminoacids offer to any form of life on this planet? 2003:F5:6F08:AF00:F87A:34E2:BFA7:387C (talk) 19:05, 19 August 2020 (UTC) Marco PB

One of those links led me to Glycol nucleic acid where the sugar skeleton is just a 3-carbon string. Sagittarian Milky Way (talk) 00:53, 17 August 2020 (UTC)

How to accelerate plastic biodegrading

I don’t really understand the biodegradablity of plastic. I live at high altitude. I did scan the articles. If I managed to greatly limit my plastic from retail purchases, could I accelarate the biodegration by putting them on my balcony in the winter to make them brittle, and leave them there during the summer to be hit by high altitude ultraviolet? But does that just turn it into powdery plastic? Also, is powdery plastic just as bad pollution as plastic bottles? Is there a next step, maybe mixing it with food waste, that would further biodegrade it? (I realize my project as currently envisioned would be pretty impractical, but the answers could still help in other ways).Rich (talk) 23:17, 15 August 2020 (UTC)

You may be able to feed your plastic to meal worms, Waxworm or termites which may have bacteria in their guts to eat some plastics. I would guess that most people will not have the space to photodisintegrate plastic. If you are going to do that you may as well use mirrors, and catalysts to speed it up, but why not just burn them if you a re trying to turn them into water and carbon dioxide? Half burning oxidation may yield something that bacteria can munch on better. Graeme Bartlett (talk) 06:39, 16 August 2020 (UTC)

Biodegradation in landfills does not immediately release the carbon dioxide into the atmosphere, which is a reason to not just burn plastic waste. Carbonization might be something to look into.^[3]  --Lambiam 07:57, 16 August 2020 (UTC)

Not an answer to the question, but here is something about additives that speed up plastic photodegradation. It does not address the issue that you end up with microplastic powder or flakes that you don't want to wind up in the oceans. If the residue goes to landfills and the plastic was biodegradable to start with, I'd be surprised though if a thorough preliminary break-up does not aid in the process.  --Lambiam 07:57, 16 August 2020 (UTC)

Well, would rendering plastic into smaller than nanoplastic, ie ”picoplastic” powder (the size of large proteins maybe)much finer than we currently see be possible? One would think such small particles would be much more “vulnerable” to sunlight and chemical reactions. (But with the large amount of plastic on earth, would the large amount of whatever those chemical reactions would be, be harmful to life?Rich (talk) 18:32, 17 August 2020 (UTC)

Those pico plastics would be very easily eaten by bacteria, as they have a large surface area and can be easily ingested. Bacteria that degrade crude petroleum would be like to consume plastic so small it would be in solution. Graeme Bartlett (talk) 00:49, 18 August 2020 (UTC)