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bhauth4d20

Tubes for this would be more expensive but could be used for piping hydrogen. Pipes for moving hydrogen would be much smaller and at high pressure.

Gas pipelines have lower losses at high pressure, which is why natural gas pipelines are typically >40 bar.

bhauth4d20

Those Mach numbers are for the relevant speed in air. I would have written that differently, but that's how the cited paper worded things.

Mostly-sealing against part of the tube before cutting it is less problematic than dealing with a large pressure difference.

Aerodynamic support and propulsion in hydrogen is less expensive than magnetic propulsion and support in a vacuum-filled tube. Building an unpressurized tube is cheaper than a tube that doesn't buckle under compressive forces. And so on.

bhauth4d20

Downside is it doesn't work. There are several reasons it doesn't work, but one is: What happens to the vaporized rock? Were you thinking it just goes up a 20km deep hole without condensing on the walls?

bhauth5d40

Using sliding electrical contacts for power is fine for current high-speed trains, but it doesn't work as well above 200 m/s.

bhauth6d30

It can't use "air" around it for engines because what's around it isn't "air".

Oxygen is much heavier than the fuel it's used with, and you'd either need liquid oxygen (which increases costs) or pressurized tanks (which would perhaps double that mass). That's still lighter than batteries, yes, but engines are also needed. Piston engines are inefficient and/or heavy, and gas turbines are somewhat expensive.

It's not that difficult to separate water and hydrogen, that's true, but processing that much gas is still rather impractical when batteries have enough specific energy. Simply condensing it in the tube is...possible, but would increase drag, especially considering density variation issues, and you'd have to deal with getting it out of a long sealed tube without leaking hydrogen.

Also, if batteries are good enough, the cost of replacing the hydrogen alone probably makes batteries better than burning the hydrogen.

bhauth13d10

For a recent example of embezzlement, in Vietnam, 1 person embezzled about 3% of the country's annual GDP.

bhauth13d20

How about burgers at restaurants, then? They're more expensive in America too.

bhauth15d40

In 2019, the average Japanese employee worked 1,644 hours, lower than workers in Spain, Canada, and Italy. By comparison, the average American worker worked 1,779 hours in 2019.

The real overtime cultures are China, India, Mexico, and South Korea.

bhauth17d20

It's not like they were the only major investor in WeWork. There was Insight Partners, for example. But I could find some other examples if you want...

bhauth17d40

To be clear, I was talking about the period up to 2019 and COVID. The cultural attitudes about investing in stocks vs money in bank accounts came from Nikkei performance before the last few years.

Since 2019, it's up 2x, but the yen went down vs the dollar and there's been some inflation. In terms of what a unit of the Nikkei can buy in America, the valuation is flat since 2019. Which might actually be a hint about what's driving the relative valuation...?

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