Science Squabbling

I would suggest it depends on what you're building your structure from.
A synclastic shape (e.g. a dome) would be great for materials that are strong in compression (concrete, stone etc) but would be difficult to achieve with a material that is strong in tension (e.g. fabrics) as you are relying on an outward load (applied from the same side as the centres of curvature, e.g. differential air pressure) to apply tension to your material.
An anticlastic shape works well for materials strong in tension as you can apply large tensile preloads to the structure using a few members in compression.

So I wrote all that, and then realised I may have missed your point. This video may be relevant, it concerns gaussian curvature and why pringle/anticlastic shapes are sometimes better than synclastic shapes.

https://www.youtube.com/watch?v=gi-TBlh44gY

Yeah, I took shell to exclude tension structures, rather thinking along the lines of concrete shells.

Yeah, classic numberphile video; where does it address whether saddles are better than domes, all I thought it said was that the Gaussian curvature of anticlastics are negative and synclastics are positive?

For some reason had it in my head that saddles where intrinsically more efficient a (concrete shell) structure than domes. Must be mistaken.

Shit, one should really rewatch a video before linking to it. I was trying to get at the inability to move between -ve and +ve (total) curvature. Intuitively (ie guessing) a loading a domestic won't try to change the sign of the curvature, whereas loading a saddle will...?

The old "Maxwell-Boltzmann distribution of weirdness" thing

Intuitively (ie guessing) a loading a domestic won't try to change the sign of the curvature, whereas loading a saddle will...?

I'll take your word for it. I always find it tricky to think of saddles.

I always find it tricky to think of saddles.

You're not alone! On re-engaging of my brain, loading a dome tries to flatten it i.e. movin from +ve curvature to 0 curvature. But, I think it depends how you load your structures. Good knows. Ask a (academic) structural engineer!

I'd assume loading both would make the curvature go to 0 as you'd be making the positive curve of the saddle flatten but only accentuating the negative curve. Can't imagine the negative curve bending to positive under loading (I know it can't but if that's our argument for saddles being stiffer...).

Alas, I'm sure it'll be covered in due course.

Could someone explain to me why running this experiment in a ruined theatre, in which, among other damage, most of the stage building is missing, is supposed to present any meaningful findings?

https://www.theguardian.com/science/2017/oct/16/whisper-it-greek-amphitheatre-legendary-acoustics-myth-epidaurus

It seems to me that all they've confirmed is that even in a much-damaged state, the acoustics are still excellent.

most of the stage building is missing

Never mind that, most of the audience is missing.

Good point, one would have to assume that the original claim was for sounds in the presence of an audience.

I don't know why people do this sort of thing, it just seems like total junk science (controversial claim for hamrack's benefit :) ).

can someone try and work out the amount of heat released during a nuclear explosion of say 50MT

does this sound right ?

The "yield" of a nuclear weapon is a measure of the amount of explosive energy it can produce. The yield is given in terms of the quantity of TNT that would generate the same amount of energy when it explodes. Thus, a 1 kiloton nuclear weapon is one which produces the same amount of energy in an explosion as does 1 kiloton (1,000 tons) of TNT. Similarly, a 1 megaton weapon would have the energy equivalent of 1 million tons of TNT. One megaton is equivalent to 4.18 x 10*15 joules.

so that means 419,000,000,000,000,000 W / s for a mega tonne 419 quadrillion watts

how much would that raise the temperature of say a cubic kilometre of air

i am just trying to work out if nuclear weapons have caused global warming

thats quite a bit of heat released when the bomb goes off

Cold dry air at sea level has a heat capacity of about 1 joule per gram per degree Kelvin.

i am just trying to work out if nuclear weapons have caused global warming

Not a chance.

here,

https://scholarsandrogues.com/2013/05/09/csfe-heat-capacity-air-ocean/

quotes heat capacity of the Earth's atmosphere at 10^21 J/K, so unless you're releasing close to a million 1 MT at about the same time you won't even scratch the surface.

Quite a bit but you’d have to compare to average solar energy hitting earth, which a quick google puts at 139,000,000,000,000,000 W
Edit: that’s at the surface, it’s obviously higher at altitude.

thats quite a bit of heat released when the bomb goes off

For comparison, annual coal consumption is about 4×10⁹ tonnes oil equivalent, and one TOE is 4×10¹⁰J, so coal burning releases about 1.6×10²⁰J every year, which is somewhere in the region of 100 times the total energy released by all nuclear explosions ever detonated.

139,000,000,000,000,000 W

I make that about 4×10²⁴J per year, or 3×10²⁵J since the first nuclear detonation. Solar gain trumps atom bombs by at least 7 orders of magnitude.

I work in a greengrocer's, will we need a Kibble balance after the kilogram vote next week?
And if so, how does it work? Can we put carrots on it?

It defines an amount of mass in terms of Planck's constant h, rather than the arbitrary and changing lumping metal in Paris. The kibble balance is just a fancy current balance you get in most undergrad lab courses.

I feel I should apologise for my work colleagues’ behaviour, since it is them to blame for all this weight scaremongering. I feel partly to blame.

That said, I’d get your scales calibrated anyway. All those femtogrammes add up and you might find yourself quids-in if it has been over-reading.

you might find yourself quids-in if it has been under-reading

ftfy.
Over-reading = buyer gets less than they pay for
Under-reading = buyer gets more than they pay for

The series of events that allowed a bit of Earth rock to form, get to the moon and then be recovered and brought back to Earth again just seems implausible to me. I'm not an astrogeologist though.

https://www.theguardian.com/science/2019/jan/25/4bn-year-old-earth-rock-found-in-apollo-14-crews-moon-haul

The debate about time travel has always seemed to me to have a major flaw. Everything is made of energy/matter
and this cannot be destroyed. If you were to disappear from one time frame a quantity of matter would dissappear too. If you then appear in another time frame you have duplicated matter.
Or am I missing something?

The abstract of the paper by Bellucci et al that is the source of the Guardian article states that "Two, currently unresolvable hypotheses for the origin and history of the clast are allowed by these data", i.e a lunar or an earth origin. Whereas the Guardian article suggests pretty unambiguously that the study says an Earth origin. So basically, not very good reporting from the Guardian, but did generate a few extra clicks through for them I guess.

Energy and matter are interchangeable. One solution would be to turn whatever mass you want to transport into energy and to put in the same amount of energy on the recieving end (which is then changed into matter).

In some sort of wormhole scenario you wouldn't be gaining or losing energy, just moving it to a different point in spacetime. No different to moving a box of bricks up and down a staircase.

Furthermore, to be pedantic energy is not exactly conserved; due to the uncertainty principle it can be "borrowed" for a short period - that is, it is only conserved over time - there may (appear to) be more or less energy in one instant compared to another. This happens when virtual particles are created. You could maybe involve that effect somehow. My quantum mechanics is very fuzzy/uncertain these days though.

Interesting, thanks.