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Cake day: July 20th, 2023

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  • Adding a fan to a sailboat might help you stop said sailboat. Adding a fan to a swamp boat is not stupid and does work.

    https://www.airliners.net/forum/viewtopic.php?t=738011

    I tried to find a figure for what percentage of the normal operating thrust a thrust reverser configuration can provide and couldn’t readily find that info. However, according to that forum, thrust reversers only really reduce stopping distance by 10% or so and are deployed primarily to help maintain control in case there is uneven braking due to poor runway conditions.

    Also, multiple sources say thrust reversers only work effectively at high speeds, and lose effectiveness at low speeds. I didn’t find an analysis on why that is the case, but it has something to do with the flow rate of air through a jey turbine being much lower at low speeds.

    A sailboat will always be at low speeds relative to the wind. A thrust reverser configuration might provide some usable thrust, but you would be much better off just using the fan directly for propulsion and skip the sail altogether. Even that is very inefficient compared to propelling against water.


  • Quantum tunneling isn’t as mysterious as popular discourse likes to make it sound.

    Quantum tunneling involves barriers to movement. Think an insulator around a wire. Electrons can freely move throughout the bulk of the metal and even just a little bit outside of the metal, but they can’t transfer to the atoms in the insulating material. However, if you have an arrangement like two pieces of metal separated by a very small bit of insulator, tunneling can become possible. Classical mechanics would say that any amount of insulator between conductors should be able to completely stop charge transfer between conductors no matter how small. However, the wave function that describes an electron’s characteristics isn’t just a single point. It is spread out a bit. If the insulating layer is small enough, sometimes the electron wave functions will span through the insulating layer and a small portion of it extends into the next conductor. This means that if we measure the charge state on both pieces of metal, every once in a while, the charge state of one will decrease at the same time that the charge state of the other increases by the value of 1 electron. Lots of factors change how often this happens, such as a strong electric field. So do we know where the electron has gone? Not specifically, but we know the charge states of the two regions and it is otherwise confined. Do we know if it is the same electron? No, electrons are completely indistinguishable, and this is actually a pretty important concept for quantum mechanics. But whether it is the same electron, or if there’s some exchange that occurs during the tunneling doesn’t really matter. We know that a charge transfer has occurred through a barrier without adding or removing energy.









  • They need to add heater packs underneath and thermocouple readings. While white is good at rejecting external thermal radiation, it is also poor at emitting thermal radiation. A white surface can be hard to keep cool if the heat comes from within. In particular, white will look like it has a much better comparitive advantage when imaged in IR than is likely to be the case in real usage conditions.

    Yellow, red, and gray may be more comfortable in practice.








  • Fermion@feddit.nltoCoffee@lemmy.world•Decaf beans
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    3 months ago

    I have found two suppliers of decaf whole bean coffees I like. Magnolia coffee co has a brazil decaf swiss water process and a decaf colombia sugar cane process. I also like Counter Culture Slow Motion. These are all medium roast.

    I actually use a blend of half decaf beans and half Jagshead Coffee Roasters Torogoz blend for my daily latte. I find that full caffeine makes my heartburn worse. I like medium-light roasts though so these options might not line up with your tastes.