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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Today at 13:26:44 »

Your conclusion was, molten gold emits more blue light than  molten silver, because gold absorbs more blue light when they are cool.

My view is that the electronic band structures don't change much on heating to the melting point(s).
And we know that silver is a good reflector.
We know (from the conservation of energy) that that means it can not be a good absorber.
And we know (from Kirchhoff's work) that it can not be a good emitter.

For red light, the same is true of gold.
But, for blue light we know that gold is not a good reflector.
It is a relatively good absorber and we  therefore know it is a relatively good emitter.

None of this is anything other than 19th century physics.
Why are you arguing about stuff that has been known for all that time?

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Today at 13:22:09 »

What's the metal?

I don't know. There's not enough information to distinguish one from the others.

But you said there was.

They are good enough to distinguish the absorption spectrum of gold from silver. If their difference in emission spectrum of gold and silver is proportional to the difference in absorption spectrum, then cameras and TV screens should be able to distinguish them as well.

They can distinguish the difference in absorption spectrum.
Is this false?
Can't you see the difference?

We can all see the difference.
But that difference is between the reflectance spectra, not absorbance or emission..

I don't think any of us can see the relevance of your original pictures of the molten metals.

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 17:56:10 »

What's the metal?

I don't know. There's not enough information to distinguish one from the others.

Let's apply some basic logic.
Cameras can distinguish between absorption spectrum of gold and silver.
Cameras cannot distinguish between emission spectrum of gold and silver.
Conclusion: emission spectrum can be different from absorption spectrum.

Let's apply some less basic logic.
Correct conclusion:
The camera doesn't have good enough colour rendering when faced with something that bright.
It is further doomed to failure because the temperatures are different.

Just because a particular piece of equipment is not sensitive enough to detect an effect, that does not mean that the effect is not there. It means you ae not using the right equipment.

All the spectroscopists know about Kirshhoff, so there's no reason to keep citing the details.
Everyone knows that an absorption spectrum typically looks like an emission spectrum.

So, they only publish examples of  the interesting cases where the rule doesn't apply- for example- with fluorescence.

Unfortunately, that means that, if you look at the publications, they will mislead you into thinking that the the spectra are usually different.

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 17:50:12 »

Kirchoff's Law of Radiation
At a given temperature, the ratio of the emissive power of a body to its absorptive power is constant and is equal to the emissive power of a black body at the same temperature.

OK.
So, it's true at any temperature.
So that means it's true when the object is red hot- mainly emitting red and IR. And it's also true when the object is so hot that it's emitting blue light.
For it to be true regardless of what wavelengths are being emitted, it must be true at all wavelengths individually.
So the spectra must be the same.
(Unless you pick something weird like a fluorescent material)

So why have you chosen to pretend that Ti doped sapphire  is similar to molten metal?

(Incidentally, if you don't disperse the Ti+++ ions into a sapphire lattice, you get Ti2O3 which is black)

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 17:42:32 »

What's the metal?

I don't know. There's not enough information to distinguish one from the others.

But you said there was.

They are good enough to distinguish the absorption spectrum of gold from silver. If their difference in emission spectrum of gold and silver is proportional to the difference in absorption spectrum, then cameras and TV screens should be able to distinguish them as well.

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 17:24:25 »

What's the metal?

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 13:03:28 »

How do you know?

The conservation of energy.
You keep trying or pretend that Kirchhoff's law doesn't exist.

But it's beside the point.
You said that a camera and monitor allowed you to do spectroscopy in the context of the emissions from molten metal.
Well- can you?
What's the metal

What's your reference?

If someone quotes newton's laws do you say "what's the reference"?

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 12:45:47 »

Cameras and TV screens were designed to represent human vision. They are good enough to distinguish the absorption spectrum of gold from silver.

Really?
If that's relevant you can tell me what metal is being cast here.

casting.png (199.58 kB . 386x245 - viewed 206 times).
So... what is it?

You are confusing between emission and absorption spectrum, because you believe that they must be the same.

The material is not fluorescing, undergoing a chemical reaction or exhibiting nuclear decay.
So Kirchhoff's law applies.
The absorption spectrum is the same as the emission spectrum.

So, what's the metal?

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: Yesterday at 08:56:56 »

Cameras and TV screens were designed to represent human vision. They are good enough to distinguish the absorption spectrum of gold from silver.

Really?
If that's relevant you can tell me what metal is being cast here.

casting.png (199.58 kB . 386x245 - viewed 206 times).
So... what is it?

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Technology / Re: How did they make the first screw?

« on: 19/03/2023 22:09:54 »

Centerless grinding does not rely on centres.

https://en.m.wikipedia.org/wiki/Centerless_grinding

Let's see you use that to create a thread.

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Technology / Re: How did they make the first screw?

« on: 19/03/2023 13:22:22 »

But if you push the tool so that the middle of your workpiece bends, the tool will keep cutting and the piece will spring back until the tool no longer touches the piece.

Are you talking about a failure of Newton's third law, or a material with an infinite young's modulus (but still machinable)?

Realistically, machinists take what's called a "spring cut" to minimise the effect.
But that doesn't eliminate it.
If you were right they wouldn't need to so... why do they do it?

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Technology / Re: How did they make the first screw?

« on: 19/03/2023 00:04:02 »

Even if the ways and the other bits and pieces were infinitely rigid and perfectly perpendicular, the workpiece would still bend because you push on it to get the cutting edge to go into the metal.
To a good approximation, the tool pressure is the same along the length of the cut, but the deflection isn't.
Using a tailstock helps.
A follow rest is (in principle) even better.

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Technology / Re: How did they make the first screw?

« on: 18/03/2023 22:22:15 »

Linearish.

A bit like cutting a cylinder on a lathe.
The further you are from the headstock, the more the workpiece bends under the load from the cutting tool.
Even if you deliberately try to cut a taper to compensate for that  you can't quite win because the correction isn't linear.
If you want really good precision, you need a feedback path. You have just invented CNC machining.

However, cutting a very good cylinder is a reasonable prospect.
If your cable is thin compared to the diameter of the winch, the diameter isn't very important.
If you put the winch a long way from the attachment point the fact that the cable is at an angle doesn't matter much.
You can, of course improve it significantly by... mounting the winch on a lead screw.
Or, you could use a second winch to move the main winch along axially.
There may be a reason why they use screws.

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COVID-19 / Re: can i have a full run down on spike protiens please?

« on: 18/03/2023 22:10:46 »

I think Ebola has spike protein
https://www.reuters.com/article/health-ebola-dc-idUKN0937961120080709

, are they god/bad/neutral

From the viruss perspective they are very good.
From the patient's point of view, they aren't.

3, how are they made

The same way a virus makes any other protein; they hijack the biochemical pathways of the cells they infect.

4, do they occur naturally

Yes; they are part of many viruses.

5, if they are bad, how do we get rid of them

Our immune system destroys them (if we are lucky)
To completely eliminate them I think we need to wait until the sun goes red giant and bakes them all.

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 18/03/2023 11:55:37 »

 Basically, the size of the cavity does seem to matter. 

That's interesting.
My question stands.

Fundamentally, how does one wall know where the other wall is in order to change its emission spectrum?

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 18/03/2023 11:52:58 »

The system is in equilibrium

That assumption has been made tacitly or explicitly  throughout the thread.
So, yes, fluorescent things are odd but gold doesn't normally fluoresce.

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Physics, Astronomy & Cosmology / Re: Do you change the spectrum of radiation inside an oven if you change its shape?

« on: 18/03/2023 11:47:57 »

Here's how molten silver looks like, around 4:35 time stamp.

Here's how molten gold looks like, around 5:30 time stamp.

It doesn't look bluer than molten silver.

Imagine thinking that you can do spectroscopy by looking at a TV picture.

Obviously, it should look bluer; it's a bit hotter.

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Just Chat! / Re: Generally speaking, how would Brits respond if...

« on: 18/03/2023 11:45:52 »

Objectively, a funeral is about the least important event in anyone's life,

It's not in their life.
Funerals are for other people. In that context they may be very important.

Objectively, watching people run round a field is unimportant.
It may be entertaining, but other forms of entertainment are available (Football has the advantage,as a participant, of being quite cheap.)

As you point out, the same is true of the Queen.

Currently, about £2 per capita per annum.

And I agree that's a small price to pay to avoid a President Truss (or President Blair or even President Corbyn).

But I can't help thinking there's a better way.
The UK's Eurovision entry will be decided in a more democratic system than our current laws.
Who knows; a real democracy might even undo Brexit.

https://www.statista.com/statistics/987347/brexit-opinion-poll/

A system with a monarch who has power but only if they don't wield it (ask Cromwell), is absurd.
It does mean we have someone quintessentially nice to send to state occasions.

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Technology / Re: How did they make the first screw?

« on: 18/03/2023 11:06:47 »

A winch and cable will give you linear motion from rotary.

That's a different clever answer from the one I was told about (see below)
I'm now waiting to Alan to misrepresent that as saying that this sort of thing was available in the stone age or some such tosh.
https://www.machinemart.co.uk/c/hand-electric-winches/

leadscrews which had been formed by magic in the 18th century.

Not by magic; by clever people.

Clever enough to realise that if you make the nut that engages with the lead screw out of a tube lined with leather, the soft leather will average out the imperfections in the leadscrew and let you cut a better one.
After a few iterations you have a really good one.

You don't need a leadscrew to cut a cylinder on a lathe nor do you need a lathe to drill a hole in a plate to make a wire drawing die.
(Indeed, while I said that wire would give you quite a good thread, a bit of varnished string would do the job.)
So; as is always the case, no magic was required; just ingenuity.

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COVID-19 / Re: can i have a full run down on spike protiens please?

« on: 18/03/2023 00:15:09 »

they have only really been discussed in the last 3 years.

By whom?