1

Plant Sciences, Zoology & Evolution / Re: Why Are Baby Animals Cute?

« on: 16/11/2023 16:32:34 »

A series on the radio about it here:
https://www.bbc.co.uk/programmes/m001sd19/episodes/player

2

Physiology & Medicine / Re: How Does The Placebo Effect Work ?

« on: 15/11/2023 12:27:24 »

It takes actual belief, something some of us cannot just conjure at will.

Placebos work even when the patient knows they're a placebo.
https://www.bmj.com/content/363/bmj.k3889

3

Technology / Re: Why is my sattellite receiver behaving oddly?

« on: 30/10/2023 11:27:07 »

I don't have satellite, but my Humax Freeview box has a repertoire of software bugs that bite at random, for no obvious reason.

4

Geek Speak / Re: Complaint about Windows 11

« on: 13/10/2023 12:15:28 »

the "end" button on my keyboard doesn't seem to do anything

The End key on my computer puts the cursor to the end on the line. I use it quite a lot, and if I pressed it one day and found it had just closed the app I was in the middle of using I'd be a bit miffed.

5

Physics, Astronomy & Cosmology / Re: Why do kettles make a whoooarr sound?

« on: 06/07/2023 12:11:35 »

The bubbles 'pop' as they re-condense, so it stops when the water reaches boiling point, and the frequency gets lower as the kettle warms because the bubbles travel further before they reach water cold enough to condense them.

Kettles with flat bottom elements are much noisier than the old ones with wound elements immersed in the water because the flat bottoms act like the skin of a drum.

6

General Science / Re: Horizontal Lightning Conductors

« on: 22/06/2023 18:03:51 »

"Skin effect" means that high-frequency components (like lightning impulses) only travel through a thin skin on the outside of the conductor.
- That is why lightning down-conductors are made of a braid of many fine wires (with a large surface area) instead of one big conductor.

All the lightning conductors I ever recall seeing are flat copper strips. Braiding it won't make any significant difference to the skin effect because the strands aren't insulated from each other, which is why radio engineers use Litz wire to reduce skin effect. (At MF/HF, above that the usual ploy is to use silver plated copper.)

Digressing a bit, a novice mistake for radio engineers is to use tinned copper wire, in which most of the current flows through the lossy plating instead of the copper, or bare copper wire, which has the same effect by the time it's oxidised. A common technique for reducing the cost of UHF feeder is to use copper plated steel for the inner conductor, because the current isn't flowing in the steel.

"Lightning impulse" -  I'll guess it's not genuine AC with Voltage swings from +V to -V many times.   I'll assume it's a single DC spike,    from  0 (volts or amps)  to +Vmax   (or +Amax ) and back to 0  over a short time interval.    I've never really looked at a Lightning strike and seen it as a plot of  Voltage (or Current)  vs.   time,   maybe it has mutiple sinusoidal components with different frequencies.

The bit highlighted is correct.

If you have a repetitive pulse waveform with a period T1, a pulse width T2, and a rise time T3, then it will have a spectrum with components spaced apart by a frequency equal to 1/T1. At frequencies which are an integer multiple of 1/T2 there will be a null in the envelope of the spectrum where the amplitude reduces to zero, and the highest frequency component will be at 1/T3.

From this is follows that if you have a single pulse, T1 is infinite, and the spectrum will be continuous, without discretely separate frequencies, and with nulls every 1/T2, up to a maximum of 1/T3. (If you had a single infinitely narrow impulse with zero rise time it would have a spectrum which is a horizontal line flat to infinity.)  In the case of the pulse in BC's reference, the rise time is ~1.2uS, so the highest frequency component you'd expect to see in the spectrum would be about 800kHz, but since the spectrum is continuous, the majority of the energy will be at much lower frequencies. (More than half the energy will be below 400kHz)

Skin depth in copper is:
Freq.        Skin depth (μm)
50 Hz   9220
60 Hz   8420
10 kHz   652
100 kHz   206
1 MHz   65.2

7

General Science / Re: Skiving

« on: 29/05/2023 21:03:16 »

The proportion of the Tool was huge, in comparison to the job/product.

It had a yellowish oily fluid in place of a milky white cutting fluid.

Anyways, i think the Thickness of the plates being cut is not allowing it to Curl.
(guessing)

See here:


Skiving.png (8.13 kB . 1717x656 - viewed 539 times)

In order for the shaving to separate, it must bend at A in order to make room for the tool, but before A it had to bend at B, and before B, C, etc. Hence the shaving curls, because once it has bent at the tip, there's nothing applying a force to straighten it again.

If you look at the video however, you'll see that the finished fin is less that half the length of material shaved off, so it must be being compressed, and I think it might be the deformation beyond it's elastic limit as it's compressed that's straightening it, but I'm not conviced I can see where the force to do that would come from either. The shaving is sliding over a smooth lubricated surface, after all.

And if it that's it, why doesn't all swarf come off the tool straight?

ps - Why is it a $64,000 question?

It's just a turn of phrase. It derives from an old 1960s TV contest in the USA where people answered questions with a prize that doubled each time. The final question was the $64,000 question.

8

Question of the Week / Re: QotW - 23.05.05 - How fast does evolution happen?

« on: 06/05/2023 22:27:17 »

& the ones who followed Chastity or observed Abstinence.

Even Children & Adult asexuals.

(Vampires...no chance!)

They might survive as individuals, but if they're not reproducing they won't survive as a lineage.

9

Physiology & Medicine / Re: What's the Evolutionary Significance of Fashion?

« on: 05/05/2023 12:21:03 »

This is Prof Steven Pinker's analysis, you'll find it in The Blank Slate or How the Mind Works, I forget which.

Firstly, high status is an evolutionary advantage: high status individuals find it easier to get a mate because it's a marker for access to resources, so people will compete for it. There are many ways in which they do this, but one of them is what Pinker calls 'Conspicuous Outrage', in a nod to the term Conspicuous Consumption, which is another means of status competition.

If people want to be accepted in society they have to conform: to 'fit in', and those that don't or won't come in for all sorts of mistreatment. This offers a high status individual an opportunity: be overtly different to everyone else and get away with it without being abused because of your status in society: Conspicuous Outrage. This then sets in place a chain reaction.

People in the strata of society immediately below the non-conformer seek to obtain some of his status by copying his behaviour and wearing the same clothes or whatever, then the level below them copies, then the one below that etc. However as soon as the person at the top sees lower status people copying him, he loses status unless he changes his behaviour and does something different again, then again, and again.

So what you have is a series of novel behaviours continually originating at the top of social groups then rippling their way down to the bottom one after the other: "fashion". The 'top' may be a pop star or a page three model, or perhaps just the 'it' kid in your class at school, the point is they have some status to assert within the group they mix among.

The problem with fashion is that it's socially destructive. Not only is it exclusive, seeking to marginalise those who don't conform, but it's also criminally wasteful to throw away stuff just because it's unfashionable rather than unserviceable. Copying others and following like a sheep rather than having a mind of your own is also fatuous.

10

General Science / Re: Should countries phase out the making of glass and plastic to save our planet?

« on: 19/04/2023 23:18:01 »

It's about time the cost of waste disposal was put on the selling price of commodities instead of at the local dump, so that you disincentivise waste instead of incentivising fly tipping.

11

Technology / Re: Can you explain this demonstration of a capacitor?

« on: 22/03/2023 14:35:48 »

I don't know where the ammeter is connected.

Yes you do, follow the wiring:


MIT vid.png (13.57 kB . 1048x591 - viewed 2432 times)

So there is at least one path from plate to plate through the ammeter.

No there isn't, the power supply has been disconnected, so the only connnection to the live plate is the insulated support on the stand, and the electroscope.

Is there any discernible pattern or explanation for the deflections shown on the ammeter during this part of the demonstration?

Yes, as above, the knob is on the live side of the meter.

12

Chemistry / Re: Why adding a fizzy drink to ice does the temp drop below the temp of the ice?

« on: 26/02/2023 18:24:47 »

I heard that

Have you checked to see whether it does?

I can see why the evaporation of CO2 will reduce the temperature, with or without the ice.

13

General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 02/02/2023 12:19:55 »

If I have a stack of sandwiches to cut, I do them one at a time, cutting them all in one just squashes them. I cut by rolling the curvature of the blade, drawing the blade across them just tears.

14

Technology / Re: Electricity Generation via treadmill. Can one person generate enough?

« on: 20/01/2023 11:37:14 »

The issue isn't whether you can produce a useful amount of power (useful for doing what? cycle lights run off a dynamo), it's whether you can do it at a useful efficiency. The human body is about 20% efficient, far worse than a combined cycle power station (55-60%), and growing the food to power it accounts for a quarter of global CO2 emissions.

15

Chemistry / Re: Strange aroma off smokeless fuel or has covid ruined my snout?

« on: 05/01/2023 16:08:21 »

A small unrelated Query...

Is Covid never ever gonna go away?

Will WE have to keep dealing with it, live & die with it like ForEver?

This doesn't bode well:


Covid.jpg (115.87 kB . 900x648 - viewed 1469 times)

16

General Science / Re: Advent calendar maths question!

« on: 15/12/2022 00:37:42 »

0,1,2,3,4,5

0,1,2,6/9,7,8

17

Technology / Re: How to learn process control system in practice?

« on: 17/11/2022 17:33:53 »

bends in the road can take the car in front out of the beam for a few seconds. So it appears to "remember" the speed of the car in front for perhaps 5 seconds

But the car in front could do an emergency stop in the 5 seconds it's out of view, can the assisted braking respond in the time left after the car reappears?

The more complexity in the control system, the more responsibility on the driver to understand it in detail, and to understand (and take action) when it hits corner cases where it doesn't do what you intend.

The more complexity in the control system, the more opaque it generally gets.

if the car in front is slowing to turn a corner, and I can see that it will be safely out of the way before I get close; the radar system (configured for sensitive mode) sees the car in front slowing to a near stop in the line of sight, and rapidly slows down my car. Flicking off the speed control for a second resolves this problem.

The problem with automation is fighting it to stop it doing what you don't want can often make more work than doing the job yourself.

18

Technology / Re: Does wi-fi harm the environment?

« on: 08/11/2022 14:15:26 »

Radio engineers have been working with radio for a century, and so have groups of professional users, if it were harmful they would have showed some signs of increased morbidity & mortality by now, but I'm not aware of any evidence of that. Concerns about safety didn't start to gain any currency until mobile phones put radio into the hands of lay people.

19

Cells, Microbes & Viruses / Re: Why are arm pit stains so difficult to remove?

« on: 25/10/2022 18:18:42 »

i suspect the deodorant to be the Cause

Me too.

I don't use deodorant, and my clothes don't stain.

20

Technology / Re: Can I get an electric gas boiler?

« on: 15/10/2022 13:24:22 »

Do you have any links ?

12 million of them in less than 10 seconds:
https://www.bing.com/search?q=domestic+chp&qs=n&form=QBRE&sp=-1&pq=domestic+chp&sc=10-12&sk=&cvid=8865F76F517743F9A56CF487A783354A&ghsh=0&ghacc=0&ghpl=