kragen

38,781 karmajoined 18 лет назад

http://canonical.org/~kragen/

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позавчераdiscuss

Your response comment saying "I have now read all of that" was posted 11 hours after I linked you to a bit over 120,000 words of notes on the topic you were asking about (according to 150 * [...document.body.innerText.matchAll(/(\d+)\s+minutes/g)].map(m => Number(m[1])).reduce((a, b) => a + b, 0) on a non-overlapping subset of the topic pages).

Some of that material is a little difficult. How did you manage to read it all so fast? I'd like to hear what you found most interesting.

As for what I'm working on right now, probably seeing the sunrise tomorrow, but see also https://news.ycombinator.com/item?id=48807996

3 дня назадdiscuss

Yeah, I do have some ideas: https://dernocua.github.io/topics/digital-fabrication.html https://dernocua.github.io/topics/self-replication.html https://dercuano.github.io/topics/self-replication.html https://derctuo.github.io/topics/self-replication.html https://dercuano.github.io/topics/digital-fabrication.html etc.

3 дня назадdiscuss

By "here" do you mean "the internet"? Are you trying to discourage people from sharing their calculations and observations with one another if they don't personally interest you?

If so, what is wrong with you?

I didn't post my notes on HN; in fact, I didn't even post them on dernocua.github.io.

3 дня назадdiscuss

I wasn't suggesting using it for shipping boxes, but rather for things like robot arms.

3 дня назадdiscuss

"Plastic" is not a material; it's a property or state of many unrelated materials. It doesn't make any more sense to say that plastic is a risk to health than to say that liquid is a risk to health or that crystals are a risk to health.

3 дня назадdiscuss

Only if you do it in an oxidizing atmosphere. Though aluminum is very liberal about its definition of "oxidizing atmosphere".

3 дня назадdiscuss

It's not that my argument is flawed so much as that it depends on some basic background knowledge about processes like corrosion and solvation. Lacking that knowledge, you're better off taking my word for it that humans are not exposed to aluminum in the environment in a different way since we started refining the metal.

3 дня назадdiscuss

That's SPIF ("single-point incremental forming"), which is mentioned in passing in my note:

> These can presumably be removed, permitting traditional SPIF processing of raw foil by sliding the point over the foil; a better alternative might be...

I don't think it's closely related to 0-_-0's "folding" idea.

4 дня назадdiscuss

I'm not sure, but I think that normally it reacts with phosphate ions to form aluminum phosphate rather than leaving the body.

4 дня назадdiscuss

Also true of teflon, aluminum oxide, and Earth as a whole. Perfluorooctanoic acid, by contrast, is not mostly harmless.

4 дня назадdiscuss

You're welcome!

It's a pretty broad term, with a lot of possibilities, but generally I mean a machine which, given a design for a machine in the form of digital data, can build a working machine of that design without further human interaction. Some imperfect approximations of the idea already exist:

- living things such as bacteria, humans, and plants: DNA is digital, true, but it's an unsolved problem to design the DNA to make a plant grow into the shape of even a chair, much less a bicycle, a lathe, or a computer.

- 3-D printers such as RepRap: they generally can only produce very limited machines without further assembly, with only very limited palettes of materials, falling far short of being able to print a whole printer without human intervention.

- ordinary compilers such as GCC: though they have already had a significant economic impact, they require a feedstock of magnetic disks or erased Flash from which to manufacture their output program, which still leaves their users vulnerable to TSMC and Western Digital. Worse, the output program depends on a CPU to run, leaving the users vulnerable to Intel and Qualcomm.

4 дня назадdiscuss

I'm not sure, but I suspect cooling requirements also enter into consideration.

4 дня назадdiscuss

Oh, thanks! You are surely correct; I was puzzled about how something as relatively inert as pizza dough could corrode aluminum at multiple microns per hour, but electrolysis can definitely do that.

4 дня назадdiscuss

And today... I shall TAKE OVER THE WORLD, Igor!

4 дня назадdiscuss

Aluminum is a major component of all soils, and soluble aluminum salts have been used in medicine and dyeing since ancient Greece, probably since ancient Egypt. They have been used in food preparation for at least several centuries.

4 дня назадdiscuss

Well, "Dercuano" sounds like "Dirk One Oh" in English, so clearly the sequel should be "Dirk Two Oh". And "Dernocua" is the properly formed vesre of cuaderno, unlike "Dercuano", which unfortunately certain people were too polite to inform me was ill-formed until too late.

:-)

Mostly I wanted a name that was short, easy to remember, and unique.

My current notes are in http://canonical.org/~kragen/sw/pavnotes2.git/

4 дня назадdiscuss

It does not, but aluminum oxide is even more of a "forever chemical" than teflon is, though less so than, for example, the nitrogen that constitutes 78% of the atmosphere.

4 дня назадdiscuss

Let's see if this is a quantitatively plausible concern.

https://en.wikipedia.org/wiki/Aluminium_chloride says orl-rat LD₅₀ of AlCl₃ is 380mg/kg, which is 20.2% aluminum by weight, so that's 77mg/kg of soluble aluminum ions. If this toxicity is due to soluble aluminum ions (rather than, say, acidity), and rats and humans are about equally sensitive to aluminum toxicity, you'd need about 3.8g of aluminum to kill a 50kg human, the ionized equivalent of 1.42mℓ of aluminum metal (at 2.71g/cc). That's 1420cm² of 10μm aluminum foil completely dissolved in the food.

Presumably you would get significant toxic effects well before reaching the lethal dose, so it would be wise to avoid exposures larger than a few tens of cm² of aluminum foil completely dissolved in your food. So it seems like the concern at least passes the first smoke test of plausibility: the total amount of aluminum present in a "grilling packet" is at least sufficient to worry about.

(Fortunately, aluminum rapidly becomes inert in the body, so we don't have to be concerned about gradual poisoning the way we do with lead and arsenic.)

The crucial question, then, is how fast the foil corrodes under cooking conditions! If it corrodes (and migrates into the food) at a micron or more per hour, then this could be a serious concern. But, if the corrosion rate is more like microns per month or microns per year, the dose wouldn't be high enough to worry about.

The fact that https://en.wikipedia.org/wiki/Aluminium_toxicity redirects to https://en.wikipedia.org/wiki/Aluminium_toxicity_in_people_o... suggests that this is at least not a recognized concern.

4 дня назадdiscuss

I do not currently have a sketch of a matter compiler, just a rough estimate that most of its parts count would probably be RAM, and that it probably needs several kilobytes of RAM.

4 дня назадdiscuss

This is very impressive!