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Joined 2 years ago
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Cake day: June 17th, 2023

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  • The carbon free rock is replacing limestone in the manufacturing process, not the sand. Sand is added to cement, along with rocks and other aggregates, to form concrete.

    From what I can tell, the way this might be bad is that the carbon free rock may not exist in significant quantity. If it does, it will be mined in the same way as limestone, so that’s just a wash not a bad thing. If the rock they need doesn’t really exist they have to buy it from someone else who makes it from readily available materials. In that case, it could be green washing, where the company can claim “our process doesn’t release much carbon compared to the traditional process” but in reality the total carbon released to create the cement - from mining to processing to pouring - could be similar.


  • Having multiple, semisolated compartments in a Hyperloop train is entirely reasonable. There’s definitely room in a traincar for the occupants of a compartment that’s on fire to move to another compartment for emergency purposes.

    Evacuation points would be defined every so often (say every few miles) such that the train could come to an emergency stop within one, seal doors on each side and let air in. This would take a few minutes, but so does landing a plane or stopping a high speed train.

    Bottom line is that fire safety is, to me at least, an entirely solvable problem. The biggest problem with Hyperloop, I think, is that given the materials for the vacuum sealed tube and the energy required to hold that vacuum, it is just so unlikely to be more efficient than a maglev. For medium distance travel, even standard high speed rail is good enough to replace planes, so we don’t need the extra speed for ~500 mile distances. For longer distances where high speed rail is super slow or impossible, such as across continents and oceans the cost of building the vacuum tube will be so costly that it would take something like a complete ban of non-renewable fuels in aircraft for it to be a consideration. Even then, I think it could end up being cheaper to develop and use renewable fuels for aircraft.


  • It is much harder for fire to exist without air. There are some self oxidizing fires, but it should be relatively easy to avoid those materials. For fires inside the vehicle, there are some existing fire protection protocols that could be followed. There have been fires on the International Space Station and they couldn’t exactly run outside either.






  • I think the point that is counter to yours is that we are nowhere near the fundamental limits of energy density for batteries. It’s probable we are near a fundamental limit for LiPo, but the point is that battery tech improves by changing technologies/chemistries. BEVs couldn’t exist at all when the best rechargeable battery tech was lead-acid, but were enabled by LiPo. Theres most likely a type of battery you can’t even imagine that has yet to be invented that could store >10x or more energy than current LiPo per unit cost or mass.



  • I’m seeing a lot of misconceptions in the replies. You have it mainly right from a very high level.

    The reason why prepreg “expires” is simply that the resin system is mixed before being impregnated into the fibers, so it starts the curing reaction immediately. These resin systems are usually designed to cure properly at high temperatures, typically 250-400F depending on end-use, but they’ll still slowly react at lower temperatures. To further slow the reaction, prepreg is kept frozen. Prepreg also has two types of expirations: “shelf life” and “out life”. Shelf life is how long it can last frozen. Out life is how long it can last at room temp.

    Theres a few issues that can happen when using expired prepreg. It can be harder to laminate since it will be too stiff and not as sticky. It won’t cure correctly causing failures in the resin.

    Expired prepreg can be recertified by testing the material for those types of failures. Check if the prepreg can fold over a certain radius and stick to a certain angle without sliding off. Cure a sample and test it to see if cured properly.



  • PocketCasts was pretty much perfect for me for a long time and recently (past couple years maybe?) they did a big update which made it noticeably worse. I tried a few other apps and they had even bigger issues. I’m still using PocketCasts and they’ve fixed some of what they messed up but it isn’t perfect.

    They have a good library of podcasts built in but also allow you to add custom rss feeds for any smaller shows they don’t have or if you have private feeds from patreon or elsewhere.