sethoflagos

Sometimes one forgets that for large, established swathes of physics, the empirical matches the theoretical with extraordinary precision. A message easily lost amongst the blizzard of disingenuous clickbait media.

Thanks, yes. Very slight differences in the numbers, but same formulae

Just spent a couple of hours trying to derive 'natural' temperature of the planet in the absence of greenhouse gas effects from basic Stefan-Boltzmann equation and inverse square law. My first engineering approximation : a small rotating sphere of something approximating to graphite gave me a temperature of 278.5 K which is not bad perhaps, but considerably higher than the figure 255 K I've seen commonly quoted. Correcting the solar influx for albedo figures of no particularly strong provenance hit the nail pretty well on the head for earth, but not so well for the moon - 270.3 K is still 20 too high. Can anyone point me towards a bona fide source reference or maybe just yea or nay the attached back of envelope calcs. Best regards, and thanks in advance for your kind attention. 'Planetary Natural Black Body Temperature.pdf

+ This for the development of appropriate beam sections etc. Plain aluminium is strongish, light, and easily machined. Ideal starting point. Maybe not so good for joints and bushings. Nylon block is your friend here. Once you're happy with the structural design, if there's a weight problem, you can start looking at alternative substitute materials (Al alloys, composites etc) to replace some of the larger components.

It's a water column. Think I'd look at a seabed pressure gauge first. They seem to work well enough on whale monitors etc.

Dickens. The entire text is 1st person singular (thou dost; thy sweet and gentle voice etc) so by parsimony...

Thy before a consonant; thine before a vowel. At least in my neck of the woods.

I've got quite fond of Llama 3.1 70B It seems quite a reasonable response to the input "provide 500 words of incoherent drivel in the style of Piers Morgan" However, for "compose a sonnet about kittens in the style of Shakespeare"... ... I can't quibble over the structure, but I can't see this winning any prizes for poetry. And "Thy eyes"?!!! Surely it should be "Thine eyes... ". Just more drivel really. I guess you have to be careful with the questions you pose, and not place too much faith in the quality of the content.

I'm sure I'm missing something only a little opaque here... ...but at least I've discovered how to select 'hidden' on Android

Consider case b) being physically realised by flow through a perfectly insulated porous plug. The pore resistance of the plug is sufficiently high for kinetic energy terms to be very small. For an ideal gas, the operating equation is d(PV) = VdP + PdV = nRdT The VdP term represents a differential loss of internal energy converted to kinetic acceleration of the flow through the plug. The PdV term represents a differential increase of internal energy due to heating from the frictional resistance opposing that acceleration. For low flow rates these two terms become equal in magnitude, opposite in sign. Hence dT = 0 I've attached a copy of my backpocket cribsheet for this sort of system. 'Isothermal' generally implies heat exchange between the system and surroundings. This case is an adiabatic one that just happens to maintain a constant temperature. The process is far from reversible due to the large increase in total entropy. Porous Plug.pdf

Consider the extensions: N (mod 2) in [1] (2 - 1) = 1 element (1/2 of population) N (mod 2*3) in [1, 5] (2 - 1)*(3 - 1) = 2 elements (1/3 of population) N (mod 2*3*5) in [1, 7, 11, 13, 17, 19, 23, 29] (2 - 1)*(3 - 1)*(5 - 1) = 8 elements (4/15 of population) N (mod 2*3*5*7) in [1, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131, 137, 139, 143, 149, 151, 157, 163, 167, 169, 173, 179, 181, 187, 191, 193, 197, 199, 209] (2 - 1)*(3 - 1)*(5 - 1)*(7 - 1) = 48 elements (8/35 of population) ie we have successive screenings via Aristotle's sieve so they're neither definite primes nor non-primes. For want of a better term, I labelled them 'potential primes' back in the days when I dreamt of being able to solve the prime pairs conjecture.

Curious possibility:

In the UK, arguably, the 2008 global banking crisis led to the fall of the Labour government in the following general election, just as the Covid crisis precipitated (in a similarly toxic campaign to the US) a landslide victory back to the left this year. Actual policies seem pretty irrelevant. It seems quite depressingly random.

Possibly. Or maybe post-covid inflation, a large section of society felt that they had more money in their pockets under the previous administration.

One major difference between the far right in Europe and the US is that the religious fundamentalists have far less influence in the former, so gender and reproduction issues gain less traction than racism and immigration. The hidden agenda is the same - economic deregulation and erosion of workers' rights.

Indeed. Neither factor can be divisible by 3.

Power is failing, so no time to check

The thought that struck me in this presentation was the distinction between theoretical research that is observation driven and that which is not. Clearly, the twin pillars of GR and QM arose out of trying to resolve observed phenomena that did not agree with the prevailing concensus theory of the time (eg photoelectric effect, orbit of Mercury etc) Today, attempts to resolve the Hubble tension perhaps falls into the same category. It seems that Sabine's issues are more associated with the the various "What If?"-type explorations that have little to no observational justification. Such as "What if the universe isn't flat" in advance of any clear observational evidence that it isn't. Similarly, what observed failing of GR is the quest to quantise gravity actually trying to address? There's no denying that such questions are interesting to speculate on. In much the same way as "What if ancient Egyptians were educated by aliens?"

There are a lot of teeth in a pretty smile 😁

Fair point, but we're talking digestive enzymes plus neurotoxins. When I looked there's over 7000 described species of assassin flies. I think it's one of them. 😀

Compare and contrast: x + 1/x = 51/2

My impression of equations of that type are dominated by: x - 1/x = 1

Force of habit. I ALWAYS do the check longhand just to be sure. (Chem Eng thing)