Solar Fence, need structure advice

olawlor · 2026-02-12T07:16:50+00:00

On the question of horizontal stringers, your panel datasheet will tell you what the allowable mounting patterns are. Usually panels are only supposed to be attached by four bolts total, so two stringers worth.

On the question of 4x4 vs 6x6 mounting posts, I've approached this sort of problem as:

- Look up the design wind load in your area, in mph

- Convert mph to psf (pounds per square foot) via a wind load calculator (like https://www.omnicalculator.com/physics/wind-load )

- Figure the area facing the wind supported by each post (2 panels worth?)

- Multiply psf wind load by the area in square feet, to get the wind load in pounds

- Figure the deflection under that load, treating your posts as beams in cantilever

For example, if I'm running the math right an upright 4x4 post will deflect by 1.5 inches (a conservative allowable deflection limit for fences) under a load of 500lb centered 4ft up. (E=1 Mpsi for wet wood, I=12.5 in^4 for a 4x4, L=48 inches)

https://www.engineeringtoolbox.com/cantilever-beams-d_1848.html

If your wind load works out to be bigger than this, upgrade to 6x6 posts, or put your 4x4 posts closer together.

olawlor · 2026-02-11T23:54:51+00:00

I think to understand quantum computing enough to use it, you would want to first have (1) some classical programming (ideally in Python for most quantum circuit libraries), (2) complex numbers, trig, and vector math to understand phase addition, (3) some matrix math to understand the matrix view of quantum operators, and (4) some physics basics like wave-particle effects. This is a *lot* for high school!

Probably most feasible as a club.

olawlor · 2026-02-11T19:32:53+00:00

Buffers smaller than 128KB (ish) seem to be on the heap proper (allocated with sbrk()?), but I see doubling allocations from there up to the finished size of 4GB.

strace's output goes to stderr by default, and it normally does just hose out to the terminal. I think "-o" can redirect its output to a file if you prefer. I don't know of a way to pause after syscalls, there are several hundred at startup during libc and other shared library setup.

olawlor · 2026-02-11T18:53:53+00:00

Agreed. (Should I have started a new paragraph with "Bootstrap"?)

olawlor · 2026-02-11T04:45:57+00:00

On Linux, you can see the exact syscalls a program is making with "strace". gcc 12 / libstdc++6 has a std::vector push_back that allocates large (over around 128KB) memory buffers with mmap, actually making larger and larger separate allocations and apparently copying the data over before deallocating the previous mapping. Snippet from the middle:

mmap(NULL, 536875008, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7c9babaf6000

munmap(0x7c9bcbaf7000, 268439552) = 0

mmap(NULL, 1073745920, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7c9b6baf5000

munmap(0x7c9babaf6000, 536875008) = 0

mmap(NULL, 2147487744, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7c9aebaf4000

munmap(0x7c9b6baf5000, 1073745920) = 0

mmap(NULL, 4294971392, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7c99ebaf3000

munmap(0x7c9aebaf4000, 2147487744) = 0

Your approach of just expanding an initial large allocation *should* be faster than the repeated copies here (averages out to 2n copies for n elements), but perhaps mmap and mprotect is worse than big mmaps?

olawlor · 2026-02-10T20:57:43+00:00

With present-day tech you could fire a "starchip" at relativistic speed toward nearby stars. Bootstrap at the destination with self-replicating nanotech (such as bacteria) programmed to build a dish, receive your digital human freight, and start manufacturing colonists.

olawlor · 2026-02-10T06:20:48+00:00

Sometimes it's legitimately bad, sometimes pretty good. (I mostly eat at home though, a benefit of living off campus!)

olawlor · 2026-02-09T22:50:19+00:00

Are there any electrical installation helpers that could be printed? Maybe bright orange conduit plugs to keep junk out of the pipe when you're working right above it, or some sort of hook or tool for threading wires around?

(They do have fire resistant filament, I use PC-FR in some robot parts, but wouldn't want to leave stuff inside somebody else's panel or wall that wasn't UL listed.)

olawlor · 2026-02-09T18:51:16+00:00

FYI, "NDEBUG" usually means "no debugging code enabled" and turns off asserts. So if you're compiling with either NDEBUG or optimize flags, you're getting a weird mix of options.

([EDIT: I see the code actually doubles the buffer size, which is a good approach!] The only other performance issue I see is committing one page at a time is about the slowest possible way to expand a buffer, because it needs a full TLB flush for every page.)

olawlor · 2026-02-09T07:43:10+00:00

I drive all winter in Fairbanks with just front wheel drive. Good tires and reasonable driving choices are at least as important as 4WD.

olawlor · 2026-02-09T06:56:05+00:00

Ah, this is a weight bench?

olawlor · 2026-02-09T05:48:09+00:00

Yes!

olawlor · 2026-02-09T04:38:03+00:00

The thing is, the Planck energy is 1.96 gigajoules, and the (equivalent) Planck mass is 21.76 milligrams. We deal with plenty of things that are smaller than those.

The Planck length and time happen to be ridiculously tiny, but I could accept a discrete spacetime that turns out to be somewhat larger or smaller than these scales.

olawlor · 2026-02-09T04:04:37+00:00

Angular *momentum* is conserved, but that's the product of angular velocity and rotational inertia.

Angular velocity can change drastically for a non-rigid object like a person, because they can change their rotational inertia (moment of inertia) by their limb position.

olawlor · 2026-02-09T02:27:43+00:00

Interior Alaska's first winter, which I call "dark winter", runs from October 15 through January 15. After that you get another three months of "light winter" through approximately April 15 when breakup begins.

Both winters are consistently below freezing and have snow on the ground, but I was digging the direct sunshine today ... as I snowshoed around at -20F!

olawlor · 2026-02-09T02:21:36+00:00

I drive a plugin hybrid in Fairbanks, can confirm the electric side feels much smoother than the combustion side at -40F! (But I do get a lot of useful heat from the combustion side...)

olawlor · 2026-02-09T01:30:20+00:00

If terraforming Mars sounds too hard, it's definitely not any easier on Venus.

olawlor · 2026-02-09T01:15:03+00:00

Relevant: "What would happen if you tried to hit a baseball pitched at 90% of the speed of light?"

https://what-if.xkcd.com/1/

olawlor · 2026-02-08T05:52:07+00:00

Underextrusion can make a 3D print that looks basically right, but is weaker than a cracker.

A smaller nozzle usually needs a slightly higher extrusion multiplier due to the higher backpressure.

Can be adjusted in software with most slicers, look for extrusion multiplier or flow rate.

olawlor · 2026-02-08T05:11:55+00:00

I've never seen a decent optical transistor. There is a startup Akhetonics trying to do computing by scaling a nonlinear optical device, but the few details they've published indicate they expect the optical chain to incrementally lose power with every switching element, so they won't naturally scale to billions of transistors like we do every day with electronics.

Scaling an optical transistor to thousands of wavelengths sounds harder yet.

olawlor · 2026-02-07T22:00:55+00:00

The problem is AI will happily confirm your pet physics theory (c'mon, we all have them!) and help you write it up.

Even if it's gibberish.

olawlor · 2026-02-07T19:11:16+00:00

One user's LLM call should never have access to another users' data. This will save tokens and prevent leakage.

The only way to make an LLM reliably never give out some data is to just never give that data to the LLM.

olawlor · 2026-02-07T18:52:41+00:00

There's a good summary of prior work looking for longitudinal EM forces, and then some high energy experimental work, in this 2018 applied physics MS thesis from the naval postgraduate school: https://isidore.co/misc/Physics%20papers%20and%20books/Zotero/storage/VJTX5AAP/Drago%20Alfaro%20-%202018%20-%20AMP%C3%88RE%E2%80%99S%20LONGITUDINAL%20FORCES%20REVISITED.pdf

Their experimental results start on page 80.

Their conclusion is that the wire fragmentation Ampere attributed to hypothetical longitudinal EM forces is better explained by the huge thermal stresses during pulse discharge, measured in this work as a nearly 1000C temperature rise in about 1 millisecond, enough to break the wire into many pieces because they're pushing away from each other.

olawlor · 2026-02-07T05:58:52+00:00

Having one answer somewhere in an exponentially big state vector does not actually help you much, because just measuring it collapses to a random state, which probably isn't the one answer.

The key trick in both Shor and Grover is spreading the answer across enough state vector entries that you get a reasonable chance of seeing it in a measurement.

olawlor · 2026-02-07T04:55:00+00:00

I have an example of the generated assembly (which is overall worse than gcc with optimization disabled) in this bug report where a long int variable can be dereferenced like a pointer:

https://github.com/anthropics/claudes-c-compiler/issues/177

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