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Cake day: February 1st, 2024

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  • Aluminum foil is very common in physics labs. And a main use for it is “baking”! To get ultra high vacuum (UHV)* you generally need to “bake out” your chamber while you pump down. Foil is used same as with baking food — keep the heat in and evenly distributed on the chamber.

    Sadly, it’s usually not food grade aluminum foil, as that can contain oils, and oils and vacuum are generally a big no-no.

    *Just how good is UHV? Roughly: I live in San Francisco, which is ~7 miles by ~7 miles (~11km). Imagine you raise that by another 7 miles to make a cube. Now, evacuate every last molecule of gas out of it. Now take a family sedan’s trunk, fill it with 1 atmosphere of gas, and release that into the 7 mile cube. That’s roughly UHV pressure.



  • ZigBee router thing:

    I’ve been happy with the SMLIGHT SLZB-06M. You can easily flash firmware, and it has PoE which was important for me. I believe it also supports Thread, but I haven’t tried this yet (and I’m not sure if it supports it at the same time as Zigbee).

    Zigbee smart plugs from Third Reality have been pretty solid in my experience, and they report power usage.

    For circuit breaker level monitoring, I have an Emporia Vue2. I have it running esphome, completely local — unfortunately this requires some simple soldering and flashing, so it’s not turnkey. But it’s been rock solid ever since flashing it. (Process is well documented online.)

    I’ve had decent luck with cheap wifi Matter bulbs, but provisioning them is finicky, and sometimes they just crap out and need to be power cycled; Zigbee bulbs (e.g., Ikea) have generally been reliable, though sometimes I’ve had difficulty pairing them initially. After power cycling a Matter WiFi bulb, it takes a while for it to respond to Home Assistant; Zigbee bulbs generally respond as soon as you power them on.

    I have a wired smart light switch from TP-Link/Kasa (KS205), and it’s been completely hassle free (and totally local — Matter over wifi). The Kasa smart switch dongles I have work flawlessly but need proprietary pairing, and I’m afraid to update firmware in case they lose local support.

    Good luck! Fun adventure :)





  • That’s…not really a cogent argument.

    Satellites connect to ground using radio/microwave (or even laser), all of which are electromagnetic radiation and travel at the speed of light (in vacuum).

    Light in a fiber travels much more slowly than in vacuum — light in fiber travels at around 67% the speed of light in vacuum (depends on the fiber). In contrast, signals through cat7 twisted pair (Ethernet) can be north of 75%, and coaxial cable can be north of 80% (even higher for air dielectric). Note that these are all carrying electromagnetic waves, they’re just a) not in free space and b) generally not optical frequency, so we don’t call them light, but they are still governed by the same equations and limitations.

    If you want to get signals from point A to point B fastest (lowest latency), you don’t use fiber, you probably use microwaves: https://arstechnica.com/information-technology/2016/11/private-microwave-networks-financial-hft/

    Finally, the reason fiber is so good is complicated, but has to do with the fact that “physics bandwidth” tends to care about fractional bandwidth (“delta frequency divided by frequency”), whereas “information bandwidth” cares about absolute bandwidth (“delta frequency”), all else being equal (looking at you, SNR). Fiber uses optical frequencies, which can be hundreds of THz — so a tiny fractional bandwidth is a huge absolute bandwidth.






  • Most of the time that leads to them dying.

    Well, squishing has a 100% chance of them dying. With a toddler and a baby, having them run loose sadly isn’t an option.

    We live in a very mild climate, and there’s under-deck and fence space around our house, in addition to bushes, trees, and underbrush — fairly suitable for a variety of arachnids. It’s not the same as indoors, and survival rate certainly isn’t 100%, but it’s not the death sentence of going from a climate controlled house to below-freezing outdoors.



  • I think large planes “look” like they can’t work because their “relative speed” is really low — that is, their speed relative to their length. We’re used to seeing birds cover tens of lengths per second, whereas a large airliner covers ~1ish per second at takeoff.

    Or not, but this always seemed like a plausible explanation as to why planes look impossible. (Though given that hovering birds don’t look funny, maybe this is a silly observation…).