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Cake day: June 14th, 2023

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  • You just have to go fast enough. The minimum speed keeping you from falling out of a circular loop is sqrt(gr), with gravitational acceleration g and loop radius r. 10m radius requires 36km/h, which might be suitable for a Jetski. Larger ships need bigger loops to physically fit, and consequently larger speeds. It’s quite surprising, but a monstrous 100m radius loop needs less than 120km/h.





  • The first part of the article triggers me. Heat in the physical sense is thermal energy. Like with other forms of energy, you need an energy difference to actually have it perform work, or you need to invest work to create an energy difference (in a heat engine or a heat pump, respectively). Just like you would letting a weight fall to the ground and lifting it back up. And cooling is removing heat, so ice cubes are actually cooling your drink.

    In a pan, low specific heat capacity is not that desirable. That’s why people use big honking chunks of cast iron to prepare food: so adding the cold food doesn’t lower the temperature too much. But the metal also gets you good heat conductivity to quickly get the heat from the stovetop to where it’s needed.

    Conversely the handle is made from materials that have low conductivity so heat gets conducted more slowly towards your skin. The higher capacity helps but isn’t that crucial: air has fairly low heat capacity but you can stick your hand into an oven at 100C without getting burned. Unlike boiling water, which has quite a high heat capacity.

    The refrigerant should have a high heat capacity to move as much heat as possible for a given temperature difference. Most systems employ a liquid-gas phase change somewhere in the cycle to transfer even more heat energy in the form of latent heat. R134a, a common refrigerant, has a heat capacity about 3/4 of that of water.

    One more thing: even if the electrical energy is completely nonrenewable, heat pumps still offer an environmental advantage. Gas power plants are fairly efficient, around 40% of the extractable heat energy gets converted to electricity. With a COP of 2.5, a heat pump would produce as much output as burning the gas in a perfectly efficient furnace. If the COP is larger, the heat pump is more efficient than burning the gas directly, and modern heat pumps usually exceed 2.5 except in the coldest days of winter. Add to that the existence of dual-cycle power plants with 60% efficiency, and the losses of a conventional furnace, and heat pumps may win even on days where the COP is slightly less than 2.



  • This was followed by Orandazuma wa Denki Unagi no Yume o Miru ka? (Do Dutch Wives Dream of Electric Eels?, Dec. 1984, PC-8801). Inspired by Philip K. Dick’s Do Androids Dream of Electric Sheep? (1968), players take on the role of a private investigator who has to track down a sex doll (called Dutch wives in Japan) that has become sentient and is murdering its lovers. The player tracks down the rogue doll by seducing all the women in Tokyo’s red-light district.

    The concept sounds awesome. The porno parody “Blade Runner” needed.



  • Sets of measure zero are unfair. But you’re right, the second line in the image is basically an eigenvector equation for Int and eigenvalue 1, where the whole point is that there is a subspace that is mapped to zero by the operator.

    I’m still curious if one could make this work. This looks similar to problems encountered in perturbation theory, when you look for eigenvectors of an operator related to one where you have the spectrum.


  • What is meant here, I believe, is (1 - Int)^-1. Writing 1/(1 - Int) is an abuse of notation, especially when the numerator isn’t just 1 but another operator, which loses the distinction between a left and a right inverse. But for a bounded linear operator on a normed vector space, and I think Int over an appropriately chosen space of functions qualifies, (1 - Int)^-1 equals the Neumann series \sum_k=0^∞ Int^k, exactly as in the derivation.

    Int is injective: Take Int f = Int g, apply the derivative, and the fundamental theorem gives you f = g. I think you can make it bijective by working with equivalence classes of functions that differ only by a constant.







  • It’s reverse: you get a board that has a floppy interface on one side and a USB socket on the other. You plug in a USB drive and the board uses a file on the drive as the floppy disk, pretending to be a floppy Drive connected to the interface. It’s a little less convenient because you have to deal with disk images but it works without moving parts.