exchemist

OK, I have to say the attempt an an analogy with DNA sounds seriously overblown. I understand of course that alloys often have a range of possible compositions and so if you know the elements present you may be able to work out what combinations are possible that could give rise to a measured density. But this stuff about "encoded information" being present in a density makes no sense to me. What are the symbols of the code? In DNA we have a 4 "letter" code: A,C,G,U, denoting the 4 base pairs. A density, being a single number, has no code whatever. Can you perhaps give an example of an alloy with, say, 3 components and show how you deduce its composition from density alone?

What is meant by treating density as encoded information? Density is just one number. Unless, I suppose, you superimpose knowledge of limits to the range of densities possible for given combinations of elements. Is what you have done something like that?

This is getting a bit silly now. The disagreement is quite clearly about the legitimacy of the term "centrifugal force", not the formula. You can specify a rotating frame of reference if you like, but if you try to apply Newtonian dynamics in a non-inertial frame you get into a lot of complications: https://phys.libretexts.org/Bookshelves/Classical_Mechanics/Variational_Principles_in_Classical_Mechanics_(Cline)/12%3A_Non-inertial_Reference_Frames/12.05%3A_Newtons_Law_of_Motion_in_a_Non-Inertial_Frame Which is why it is in most circumstances not a good practice.

This is interesting. I found this article: https://www.ncbi.nlm.nih.gov/books/NBK127546/ according to which people with the A version of the gene do not produce odour precursors while those with the G type do. The A type is very highly prevalent in people of East Asian descent and in fact only 7% of them use deodorants. By contrast, those of European or African descent usually have the G type and so it is these societies where deodorant use has become the norm.

That article makes clear that a similar process is not expected to occur on Earth, or not until a billion years from now.

Why would water suddenly start escaping into space if the temperature of the upper atmosphere is lower than now, as it would be in a runaway greenhouse scenario? The proportion of water molecules with a velocity > escape velocity would be decreased, not increased. And what new mechanism would cause water to disappear into the ground?

My point is there is a huge difference between a slight smell of sweat or traces of body fluids in the groin, for which washing is quite sufficient, and the powerful odour of unwashed and non-deodorised armpits. If you just wash your armpits, and don't use deodorant, they smell really rank after as little as 12 hours. Nobody's groin ever smells remotely like that.

Why then does nobody bother with deodorant for the groin?

Sure, it is rather speculative. But the possible correlation of the appearance of the enzyme with the rise of the primates is an interesting finding.

OK so that shows the groin area does not produce body odour in the way the armpit does, right?

Well nobody puts deodorant on their groin, do they? And I’ve never had any complaints.

Hmm, I see the link actually says the space station was designed to simulate lunar gravity. As to the radio clip you linked, well I think you have got deGrasse Tyson bang to rights! 😆 How very sloppy of him. Sort of fits with my feeling he tends to be a bit glib. it must be very annoying for the film makers to go to the trouble of getting something scientifically right (God knows, it is rare enough for them to bother), only to have it traduced by a public science “personality” who should know better. By the way I rather like the “Kardashian Index”. I was delighted to see that, though their Exhibit A is Tyson, Exhibit B is Britain’s Brian Cox. He is someone I have always found irritating -and again, glib - so I’m glad to see I’m not the only one who finds him so. But his index is an order of magnitude lower than N deG T. Should this have a logarithmic scale, perhaps?

There do seem to be rumours about him farting uncontrollably, e.g. in a recent court appearance.

Erm, that would be an angular velocity of about 0.1/sec, wouldn’t it? So an acceleration ~ 1.5m/sec2, about the gravity on the moon. Is that right? But where do you get the radius of the space station from, and the rotation rate? And when and where did Tyson make this claim? I can’t seem to find a reference to it.

I'm not aware of any such reports. Please don't start a silly discussion about UFOs based on crap YouTube videos.

It seems to me St. Paul is to blame for -ve Christian attitudes towards sex. There's practically nothing in the OT or the gospels about it being "bad". It's a misconception, (hahaha), to think that the Fall or Original Sin had anything to do with sex. That's just been read into it, by puritanical-minded people, later.) Unfortunately St Paul has had almost as much influence as Jesus on the way the religion has developed. Having said all that, it is natural that sexual activity should have been the subject of control by society, because the human baby is very demanding to take care of, for a very long time indeed. So creating babies is something that should be done responsibly, in a stable environment in which they can be reared satisfactorily. Sometimes I think that we, living as we do nowadays in an era of easy access to contraception, don't recognise why there had to be social means of controlling sexual activity in the past.

Yes but the overall genital area with body hair won’t have such a low pH. And, if it comes to that, I am not aware that men produce a body odour smell from the groin either. Only from the armpit. So I’m wondering if there a different secretion there , or if there is another reason why Staph. hominis can only thrive in the armpit? Actually, thinking a bit more, one obviously unique feature of the armpit is the huge amount of sweat secreted. There must be a lot of eccrine glands there. Although, as I understand it, it is the apocrine glands, in the hair follicles, that secrete the smell precursors, the sheer amount of sweat and almost continual dampness of the armpit may be what provides the environment for Staph. hominis to do its thing there, rather than elsewhere on the body. But I'd still love to know what the bacterial population of the man who didn't wash ended up being.

You don’t want to use a material that is within 100C deg of its melting point. It will have lost all its strength. And steel, being a metal, is a conductor of heat, which would be catastrophic. Anyway, have a read. There’s quite some discussion of the options for various materials and the challenges involved.

According to the attached NASA slideshow, temperatures reach 1700C for slower, "flying" type re-entry, but hotter for capsules that make a "ballistic" re-entry. It's quite interesting for you to read. They have, not surprisingly, given quite a bit of thought to this topic. daryabeigi-NMS talk-2c.pdf

This prompts two further reflexions: 1) My experience is the genital area does not become smelly like armpits, even though no woman I've been to bed with (sample size 13) used any deodorant on that area of the body. Why is that, if both armpits and genital areas have these apocrine glands? Or does Staph. hominis for some reason only inhabit the armpit, and if so why would this be? 2) I read a year or two ago about a man who conducted an experiment by not washing as modern people do but simply allowing nature to take its course. He claimed that after a couple of weeks of being smelly, the smelly gradually reduced until it was no longer noticeable. When I heard of this originally I assumed he had just got used to his own smell, but now I wonder if there might have been competition among skin bacteria that eventually resulted in the Staph hominis population stabilising at a low level, due to being checked by rival groups of bacteria that can't grow when one washes daily in the usual way.

Graphite is often used, as it conducts heat well only along the plane of the structure and has a very high sublimation point (it doesn't melt), over 3,000C. Something that melts at 660C will lose mechanical strength well before then and will just disappear. I really think you need to work harder on this aspect.

Al will be a hopeless choice: it melts at 660C. Also, being a metal it conducts heat! You will need something far more refractory that is also a good insulator (e.g. even tungsten won't do). I know nothing about 3D printing but I fear your idea may come to grief on this point, if you can't find a high melting point insulator that can be worked by your 3D printer.

So 3D printing is the key feature. I see. What material would it be made of then, that can be 3D printed (I assume ceramic tiles cannot be)?

Why would it be less laborious to replace this proposed ablative surface than to replace thermal tiles?

Actually, this is quite interesting. There was a paper in Nature in 2020 about the bacterial enzyme responsible for generating these thioalcohols that are mainly responsible for the smell: https://www.nature.com/articles/s41598-020-68860-z They also did some work to project back in time to estimate the point at which this enzyme evolved in the unique bacterium responsible (Staphylococcus hominis), finding it may have been around the time the primate lineage first appeared, c.60m year ago. From this they suggest there may have been evolutionary selection pressure encouraging this enzymatic function, in the symbiotic relationship between this bacterium and the primates that were the ancestors of modern Man. So the suggestion is that smelly armpits were originally a reproductive advantage. Here is the relevant paragraph from the Discussion section of the paper: This discovery raises important questions about the role of odour production in the evolution of modern humans. The emergence of an enzyme present in bacteria found in the human underarm with unique activity to catalyse production of 3M3SH suggests selection pressure for the production of odours over an extended period of evolutionary time. This was presumably driven by an evolutionary advantage for both the host (primate, human), that actively produces the odour precursors for no other apparent physiological reason, and their microbiota, which converts them to volatile odorous molecules. Here, we have identified a definite substrate-product relationship, namely the conversion of specific thioalcohol precursors by malodour producing staphylococci. We show that S. epidermidis unequivocally does not metabolise these precursors, despite being the most abundant Staphylococcusspecies present in the axilla. Could these thioalcohol precursors secreted by the apocrine sweat glands be significant for the ecological success of S. hominis in the human axilla? This raises important and as yet unanswered questions regarding the mechanisms that govern the structure and composition of the axillary microbiome. Early man (and woman) may have found the smell a turn-on. To this day, perfume preparations commonly include "musky" elements. (One of these is ambergris, which is basically shit from constipated whales........)