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Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 01/09/2024 22:57:24 »

This means they can collect a lot more photons, under the same conditions.

Er, sort of. What matters is the brightness of the image, and for a given object this is principally determined by the ratio of aperture to focal length of the lens. This is conventionally specified as an inverse ratio f/n and for most cameras the largest aperture is around f/2, fairly close to the fully dilated human eye at f/3. Telephoto lenses bigger than f/4 are a bit unwieldy.

I heard that the human eye requires two photons to strike the same cone cell within a short period to register a flash of light.

Interesting. The same applies to photographic film. You need two visible photons to strike a single grain in a short time for a latent image to form. Under very low intensities, this causes "reciprocity failure" where the apparent sensitivity of the emulsion decreases with decreasing image brightness.  Astronomers used to "pre-fog" their plates to increase sensitivity - something of a black art probably lost nowadays thanks to  CCD imagers.  It also explains why fine grain photographic emulsions are less sensitive (typically ASA 50 - 64) than coarse-grain (ASA 1000) materials.

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Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 30/08/2024 13:17:31 »

Given that single photons produce visible Cherenkov phosphenes, the minimum detectable event is probably of the order of 10^-18 seconds.

This is quite different from the subsequent processing time required to distinguish between events. Raster-scan television screens and mechano-optical cine projectors produce an image of continuous motion if the sampling frequency exceeds about 16 frames/second, and even when individual cine frames are clearly blurred (say taken at 40 mS intervals)  the projected "moving image" can appear as sharp as a still photograph.

LED lights driven at < 10 Hz may appear to flicker but at > 20 Hz the light output appears continuous.

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New Theories / Re: How do we acquire language?

« on: 28/08/2024 18:31:05 »

Never mind the other bullshit, but Sultans of Swing has to be the best rock number ever. Closely followed by Love Shack.

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Just Chat! / Re: Is there a universal moral standard?

« on: 20/08/2024 11:14:14 »

What's immoral about a mosquito procreating? Or a parasite colonising a new host? People procreate, and some even want to colonise other planets. What's the difference?

Fact is that different species have conflicting goals, so no possibility of a universal moral standard.

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New Theories / Re: What's the unit of Torque?

« on: 19/08/2024 18:32:30 »

You are just adding to your own confusion and helping nobody. Force x moment arm = torque. What's the problem?

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New Theories / Re: What's the unit of Torque?

« on: 18/08/2024 12:26:26 »

If you put down Gemini and pick up an elementary physics textbook, it will tell you that I = Σmr², as every schookid knows.
Why do you waste your time consulting a long-winded mechanical idiot?

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New Theories / Re: What's the unit of Torque?

« on: 15/08/2024 21:36:43 »

I think you need to first understand what the meaning of a concept as it's currently understood by most of its users.

Not on a science forum. There are formal and precise definitions of important words like torque, power, energy, velocity, speed, exponential....which are not currently understood by most of the people who (mis)use the words.

I think the correspondents in this forum are well acquainted with Newton's laws, even if the people who feature in some videos aren't.

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New Theories / Re: What's the unit of Torque?

« on: 13/08/2024 18:17:14 »

[Quote ]from: Bored chemist on 11/08/2024 23:44:06
The units of both are mass length squared per time squared.

this is so wrong.  It seems to presume that energy and torque are the same thing, and then applying a relativistic notion of mass-energy equivalence to torque.

No, it's purely classical.

Work = energy = force x distance, MLT^-2 x L
Torque = force x distance MLT^-2 x L

Which is why you can measure torque with a spring.

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New Theories / Re: What's the unit of Torque?

« on: 11/08/2024 16:52:55 »

I think one would have to do an integration of the torque over the full winding cycle as the torque will not be constant.

As the tightening torque increases with each turn of the key, I think the final torque equals the stored energy, same as when you stretch a bolt by tightening it. The difference is the much smaller hysteresis and energy loss of a spring.

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Just Chat! / Re: Is there any greater ******** than Elon Musk?

« on: 07/08/2024 23:00:24 »

Elon should be barred from twitter

But he owns it, idiots subscribe to it, and journalists rely on it as a substitute for news.

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New Theories / Re: what is temperature?

« on: 07/08/2024 16:30:26 »

Whatever else you do in life, please do not attempt to learn or teach physics from Gemini. Utter crap.

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Technology / Re: Nuclear generation produces green energy?

« on: 06/08/2024 15:58:11 »

The statutory occupational dose limit is 20 millisievert per year, 20 times the "public" limit. When designing any publicly-accessible facility you need to adopt a dose constraint of about 0.3 mSv/year or less.

Submarine crews and shore maintenance personnel are monitored and rotated to keep their dose "as low as reasonably practicable" given the inevitable exposure associated with their employment, but the reactor shielding for any vehicle is necessarily a compromise between weight and safety, which is why there are no nuclear-powered aircraft. To bring the reactor into a permanent civilian facility you would need to build a whole lot more shielding, which demands concrete and steel, which consume a lot of fossil fuel. On patrol, of course, sea water is a very effective and zero-cost radiation shield when the reactor is running at full steam, so you only need to shield the forward bulkhead (assuming the reactor is at the stern) against maximum flux. You can't run the part-shielded reactor at full chat in a crowded harbor, but you'd need to if it is intended to supply the electricity grid.

Civil aircrew generally receive about 4 mSv/yr but there is some debate over whether this is an employment dose since (a) the source is entirely natural and  uncontrollable and (b) it's still within the range of natural background doses to which some populations are exposed (up to 8 mSv/yr in parts of Cornwall, and a lot more in some other countries)  with no evidence of harm. So we have monitoring programs and advisory crew rotation but so far, no lawsuits.

Nuclear submarines generally work at about 200 MW, which won't make much impact compared with Drax (biomass) or any of the coal, nuclear  or gas stations opened in the last 50 years, which run at 2000 - 4000 MW. You could probably run a big hospital from a submarine.

And rerturning to acsin's plan, why build a submarine anyway? A land-based nuke would be a lot cheaper, though still uneconomic.

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Just Chat! / Re: Where do I get my confidence to challenge established theories?

« on: 04/08/2024 18:07:54 »

Non-mainstream ideas are less likely to get public funding.

One of the great flaws of public funding, alas. Your brilliant hypothesis and amazingly simple experiment will be judged by lesser minds who prefer to sit on committees rather than get their hands dirty.

The way to get research funding is to find a private company with a problem whose solution will make money. 

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COVID-19 / Re: Was the Covid Pandemic Panic justified?

« on: 01/08/2024 20:24:40 »

Yes, the vaccines did absolutley bugger all for herd immunity,

Because vaccination is preventive - exactly the opposite of primary herd immunity. Secondary population resilience occurs when you have vaccinated enough people that the R value falls below 1. 

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General Science / Re: Is the Curie Effect Reversible

« on: 30/07/2024 15:27:28 »

Some confusion, I think. A permanent magnet will become permanently demagnetised above the  Curie temperature but a piece of soft iron simply changes from ferromagnetic to paramagnetic, and this change is reversible. So you could just wind a coil around a chunk of soft iron to make a precise thermostat switch. The clever bit is engineering the CT to whatever you need for soldering, but I notice that current Weller adverts are all for gas soldering irons or electronic variable-temperature units.

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New Theories / Re: Universal Utopia? What's The Universal Terminal Goal?

« on: 22/07/2024 17:41:35 »

Nor, it seems, has anyone else.

Consciousness has intrigued and baffled philosophers. To begin, we must define and describe consciousness. What to include in a complete definition and description of consciousness?

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New Theories / Re: How does light propagate? By what means does light get from Point A To Point B?

« on: 19/07/2024 17:53:12 »

the underlying principles that led to the concept of wave-particle duality are still valid and essential for understanding the quantum world.

That statement is about as wrong as it can be, and underlies about half of the misapprehensions that find their way into this forum.

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Just Chat! / Re: How did the world seize up?

« on: 19/07/2024 17:50:01 »

First rule of any business: if you entrust critical processes to a third party, you will lose all your money.

And if the third party is a self-optimising AI system, you have no enforceable redress.

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Question of the Week / Re: QotW - 24.07.26 - What can I smell when it rains and does it depend where I am?

« on: 19/07/2024 17:42:37 »

I heard that people in the UK can?t smell when it rains,but us Americans can.

The chemistry and olfactory physiology are the same but most of the UK surface is moist most of the time, so we get habituated to it most of the year.

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New Theories / Re: How do we measure the energy of a photon?

« on: 16/07/2024 15:52:27 »

Personally, I would not use "drivel" when addressing someone's attempt to put forward a physics theory. I would point out the incorrectness of the attempt and how it could be improved if possible.

I did. The only cure for drivel is to abandon it, apply common sense, and learn some elementary physics - in this case, that you can't see the TV picture if you close your eyelids.