1

General Science / Is the Curie Effect Reversible

« on: 30/07/2024 14:50:14 »

So this website says that the Curie Effect is not reversible: heating above the Curie point results in a permanent loss of magnetism.

This seems to contradict the operation of the Weller soldering irons that I spent my whole working life using: they have bits with a magnetic pellet that it releases a spring-loaded armature to open the switch contacts when the bit reaches it's set temperature and attracts it again as it cools.

Reading Wikipedia, they make no mention of whether it's reversible or not, and Chat GPT starts by saying that it is, then agrees with the site that says it isn't, then when I point out it's contradicting itself says that there are two Curie Effects: one reversible and the other not.

I see that the original site makes note of a separate effect that's not the Curie Effect, but which causes a reversible loss of magnetism which is progressive not sudden, but I'm sceptical that's what Weller are using, as without a sudden loss at a particular temperature, the switching point would be dependent on the armature spring as well as the bit, and much more difficult to calibrate. Weller call their system Magnastat without reference to Curie, and although they don't explain in any detail how it works, they do refer to a change in characteristics at a specific temperature.

2

Physiology & Medicine / What tissue is this?

« on: 23/07/2024 13:33:59 »

Behind my ear is a groove where the arm of my spex rests. The force it exerts must have all on to be even as much as a gram, so you'd think the tissue it's making an impression in would be soft to the touch, but it ain't so. If I press it with my finger it's so hard and permanent it feels as if someone has machined the groove into my skull.

Yesterday I found a similar groove in my knee where it had been resting against the table leg, and again, it felt so hard it's as if the groove has been filed into my kneecap even though it can't have taken much more than an hour or so to develop. I didn't notice how long it took to disappear again.

What tissue's developing these impressions? It's not soft like pitting oedema, the way sustained gentle pressure deforms it but sudden hard pressure doesn't makes it seem like a non-Newtonian liquid.

3

General Science / Why don't hands get sunburnt?

« on: 17/07/2024 15:00:41 »

Mine seem immune.

4

Physiology & Medicine / Going Deaf

« on: 08/07/2024 14:01:59 »

As deafness develops, does the threshold of damage rise in step with the threshold of hearing, or does the safe zone between loud enough and too loud shrink?

5

Physiology & Medicine / What Causes Saccadic Dysmetria

« on: 24/06/2024 17:10:10 »

??

6

General Science / Do germinating tomatoes kill off competing plants?

« on: 10/06/2024 11:52:32 »

What's going on here, it looks like the 'winning' shoot kills off all its competitors.
https://www.youtube.com/shorts/6gRBjN9SiTw

7

Physiology & Medicine / Can General Anaesthetics Cause Diabetes?

« on: 05/02/2024 11:53:09 »

As per the title.

8

General Science / Firefighting

« on: 11/01/2024 12:51:28 »

I don't understand how this works, why is the air that gets drawn in depleted in oxygen?

https://twitter.com/gunsnrosesgirl3/status/1745395156226896197

How is it any different to drawing the fire by injecting the exhaust of a steam engine into the chimney?

9

General Science / How many square metres in 10km^2

« on: 03/11/2023 11:37:22 »

a) 10,000?
b) 10,000,000?
c) 100,000,000?

10

Geek Speak / How to make VLOOKUP tell the difference between zero & blank

« on: 28/10/2023 16:23:05 »

Excel 2010

I need VLOOKUP to tell the difference between a zero and a blank because MAX, MIN and AVERAGE count zeros but not blanks. I'm also plotting the same looked up data, and I could do for the graph to leave a gap where there are blank cells too, instead of joining the ends with a line. Simply replacing zeros with "" won't work, because the data contains zeros. At the moment the cells that would be blank have been filled with NA, but AVERAGE won't put up with that either.

I'm plotting data on a graph that has an x axis that's continuous, but the data in the table is discontinuous, with gaps in it. (There are nearly half a million lines in the table, and the graph needs to be plotted using samples selected from it at random, so anything that involves any manual faffing around is out of the question.)

11

General Science / BODMAS

« on: 12/09/2023 16:53:12 »

Has anyone else noticed this:

Bodmas.png (577.58 kB . 788x385 - viewed 302 times)

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General Science / Broad (Fava) Beans: Difference between frozen & fresh

« on: 24/08/2023 16:32:27 »

 When cooked, frozen broad beans are smooth, green and hard, and the cooking water turns black, but fresh ones are wrinkly, purple and soft, and the cooking water turns red. Why the difference?

And why are the last bag of frozen beans I bought purple, soft and wrinkly unlike all the previous ones?

(The cooking water's clear when it's drained off, it turns coloured if it's left a few hours.)

13

General Science / Pneumatics Question

« on: 06/08/2023 17:28:06 »

About 13 years ago (so my recollection of the details is a bit hazy) I inflated a cycle tyre quite rapidly after mending a puncture using a Zefal plastic pump similar to this, which has a small threaded brass bush for the hose moulded into the end of the cylinder.

Whilst I don't recall the end of the pump getting any hotter than usual, on this occasion the brass bush got hot enough to soften the plastic until the pressure (~80-90 psi) pushed the bush out of the end of the cyclinder. What intrigues me is why the heat was so localised, if the whole end of the pump had softened to that degree it would have inflated like a balloon and burst. The outer surface of the bush was heavily knurled to give it a key, so it wasn't going to come out lightly without the plastic softening.

Zefal describe the plastic as a 'technopolymer resin', so there's no prospect of looking up the melting point, but some plastics have an upper 'useable' temperature below 100C. It seems possible that the heat was getting funnelled toward the outlet along with the air, and it must be travelling at quite a high speed, so 'wind warming' would be quite significant. Pressing a finger over the outlet, I can burn it in a couple of strokes of the pump without the cyclinder end even getting warm.

Any thoughts?

14

General Science / World's First RT Superconductor

« on: 27/07/2023 14:36:37 »

It seems the Koreans have just discovered the Holy Grail:
https://arxiv.org/abs/2307.12008
https://arxiv.org/ftp/arxiv/papers/2307/2307.12008.pdf

15

General Science / Horizontal Lightning Conductors

« on: 19/06/2023 13:41:35 »

If you look closely at this building you will see that the lightning conductor runs horizontally in a ring around the base of the roof just above the gutter. There are numerous strips coming down to it from the top of the roof, but none connecting it to the ground.

Eh?

16

Geek Speak / Why is Windows 7 still updating 3 years after updates were discontinued?

« on: 17/06/2023 11:04:19 »

I switched my old laptop on for the first time in a year or so and it booted up with

"Installing Windows Updates, Do Not Turn Your Computer Off"

and this with my router switched off.

17

General Science / Water in Space

« on: 07/06/2023 16:02:25 »

I've lost count of the number of times I've seen them playing around with stunts like this, why the hell aren't they fazed about thousands of water droplets floating around in the air and getting into the electronics?

https://twitter.com/Rainmaker1973/status/1666395724194488328

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General Science / Skiving

« on: 28/05/2023 14:37:57 »

The 64,000 dollar question is why is this 'swarf' coming off the tool perfectly straight and flat when any other swarf comes away in a curl?

https://twitter.com/engineers_feed/status/1662762998404902913

19

General Science / Dry Docks

« on: 23/03/2023 13:10:42 »

Having seen ships in dry dock from time to time, and been struck by how precarious the supports looked, I'm having difficulty in being surprised at the "capsize" of the Petrel.

The system I recall seeing has the keel, and I presume the majority of the weight, supported on blocks on the floor, with props at the sides holding the ship upright. With the ship balanced on the keel and minimal load on the props, since they were wedged and in compression only it would take relatively little force from a gust of wind to momentarily release the compression at the windward side, at which point all the props fall out.

It looks like there's about 900m² of windage, which would give about 20 tons at 45mph, perhaps that's enough if the props were put in carelessly, especially if there are repeated nudges from repeated gusts over a long period of time.


Petrel.png (4.86 kB . 707x677 - viewed 1174 times)

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General Science / Do You Dream in Monochrome or Colour?

« on: 08/12/2022 12:22:00 »

On Radio 4 this morning someone was saying that in the days of B&W TV only 9% of the population dreamt in colour, but now in an era of colour TV the ratio is reversed. That reminded me of a news story a few years ago in which a blind man who had just been given an operation to restore his sight said that he was now dreaming in colour instead of B&W.

At the time, that set me wondering about whether I dream in colour or B&W, and after much thought I realised it's neither. My dreams are like memory, they occur in terms of salient points: if I think of a rectangle or a circle they're not in in colour or B&W, they just 'are', unless I think of a no enty sign, in which case I see a red circle and a white rectangle.

In the most recent dream I recall, I was talking to someone. I don't know who I was talking to, what they said, or what they looked like, but they were trying to show me something, and I don't know what they were trying to show me either, I just recall telling them that I couldn't see it because I was having an ocular migraine.

Then I woke up and found I was having an ocular migraine. That's all I rememeber/saw, because that's all that was salient.