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Clever guy (lemmy.world)
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[-] bjoern_tantau@swg-empire.de 155 points 1 month ago

A high voltage electric fence. At some point even standing in front of the thing is enough.

[-] SzethFriendOfNimi@lemmy.world 48 points 1 month ago

Air only has so much resistance itself. High enough voltage and the closest path to ground is where the charge will go.

Just like with Lightning

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[-] absGeekNZ@lemmy.nz 16 points 1 month ago

At approx 3kV/mm, you would have to be pretty close to a 10kV fence.

Humidity plays a big role as does the frequency that the fence is running on. But you would be pretty safe standing a meter away, on that dry sunny day in the picture.

Also above a point, the high voltage causes the conductors to buzz.

[-] frezik@midwest.social 12 points 1 month ago

Dry? It was a carribean island, right? Probably humid as fuck.

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[-] ArbiterXero@lemmy.world 14 points 1 month ago

With enough voltage, everything is a conductor.

[-] Grumpy@sh.itjust.works 13 points 1 month ago

I have a 10KV electric fence. 5KV to 15KV is typical electric fence voltage in a farm or bear prevention fence. Can't feel a thing unless you actually touch it.

They are also not lethal. Very low current, just very high voltage. So it only hurts like fuck, but won't kill a human, cow, or any other mammal that touches it.

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This is why you should never try to remove a tree from a power line yourself.

Electricity always takes the path of least resistance back to the source. A tree, and possibly your body, may end up being the "path of least resistance".

You won't know if YOU are the path of least resistance or it the line is even energized until it's too late.

[-] sugar_in_your_tea@sh.itjust.works 9 points 1 month ago

Yup, this is why I shoot fallen tree limbs with a shotgun.

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[-] Lev_Astov@lemmy.world 95 points 1 month ago* (last edited 1 month ago)

At 10kV, a random stick would be all it takes to start an arc. He knows what he's doing.

[-] stupidcasey@lemmy.world 47 points 1 month ago* (last edited 1 month ago)

True, True… Hay who thought it was safe to run 10,000V Wire through a flammable overgrown jungle?

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[-] OutlierBlue@lemmy.ca 62 points 1 month ago

Just because you're very good at one thing doesn't mean you're good at another. Sometimes the further you go down one path, the less you know about everything else.

[-] ceenote@lemmy.world 10 points 1 month ago

He must be a real good paleontologist to forget that wood is a bad conductor.

[-] OutlierBlue@lemmy.ca 14 points 1 month ago

He was so good that John Hammond sought him out to invite him to the park to check it out before it opened.

[-] Moobythegoldensock@lemm.ee 8 points 1 month ago

Hammond didn’t pick him, the insurance company did. The company insisted on only him, likely because he was a notorious skeptic who would be able to look past the sensationalism of the dinosaurs to let them know a realistic risk assessment. The dinner scene where he and Ellie criticize Hammond is exactly why they wanted him there.

Point being, no indication is actually given that he was smarter or more published than the others in his field, because that isn’t really what the insurance was after.

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[-] SharpieThunderflare@lemmy.ca 58 points 1 month ago

IIRC, he was messing with the kids and knew it was off because the lights were off. He proceeded to put his hands on it and convulse wildly as a joke.

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[-] LEDZeppelin@lemmy.world 50 points 1 month ago

Clearly his PhD is not in electrical engineering or biology

[-] The_Picard_Maneuver@lemmy.world 37 points 1 month ago

It's actually a PhD in trombone. Someone misheard it one time, and nobody has ever thought to follow up.

"Oh, Alan? Yeah, he has a doctorate in bones or something."

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[-] Th4tGuyII@fedia.io 49 points 1 month ago

As someone who has worked with academics, the more specialised the person, the less common sense they seem to hold onto.

As such, if this was outside their PhD specialisation, then it'd absolutely make sense that this wouldn't occur to them.

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[-] captainlezbian@lemmy.world 44 points 1 month ago

Yeah that’s people with PhDs in my experience

[-] finitebanjo@lemmy.world 9 points 1 month ago

Yeah, in this case it's so high voltage that the resistance of the dry stick wont mean as much.

[-] Bertuccio@lemmy.world 43 points 1 month ago

I invite you to touch an electric fence with a stick then.

[-] Mr_Blott@feddit.uk 8 points 1 month ago

I've installed a few, and you do have to test them somehow.

Best way is a long piece of grass, hold it about 30cm down and touch the other end to the fence. Most you get is a little tingle

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[-] Damage@feddit.it 42 points 1 month ago

Wet wood from the ground is probably a better conductor than dinosaur scales

[-] SpaceNoodle@lemmy.world 8 points 1 month ago

Did dinosaurs have scales?

[-] Steve@startrek.website 29 points 1 month ago

They couldn’t even read music at all 😞

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[-] Evil_Shrubbery@lemm.ee 24 points 1 month ago

I dont think so, bananas are a relatively new thing iirc.

[-] MySkinIsFallingOff@lemmy.world 10 points 1 month ago

Mmmmmh, nom nom nom nom.

That's exactly the right amount of dopamine hit I'm scrolling for. Now I can turn off my phone and roll over to sleep. Thanks bud 👌

[-] Damage@feddit.it 7 points 1 month ago

They did in Jurassic Park

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[-] MalReynolds@slrpnk.net 35 points 1 month ago

I don't remember the scene, but personally I'd test an electric fence with a nonconductor. You'll probably get some sparks but won't die. You do you, ppl in this thread.

[-] Aceticon@lemmy.world 33 points 1 month ago* (last edited 1 month ago)

Well, I have an EE Degree specialized in Digital Systems - pretty much the opposite side of Electronic Engineering from the High Power side - and I would be almost as clueless as that guy when it comes to testing a 10,000V fence for power.

On the other hand I do know a lot of interesting things about CPU design ;)

What’s the most interesting thing you could tell us about CPU design, something that a layman could appreciate.

You should know as a software developer I write inefficient code and appreciate all the extra clock cycles we get these days haha.

[-] Aceticon@lemmy.world 29 points 1 month ago* (last edited 1 month ago)

First a fair warning: I learned this stuff 3 decades ago and I've actually been working as a programmer since then. I do believe the example I'll provide still applies up to a point, though CPUs often implement strategies to make this less of a problem.

=====

CPU's are internally like an assembly line or a processing pipeline, were the processing of an assembly instruction is broken down into a number of steps. A rough example (representative but not exactly for any specific CPU architecture) would be:

  • Step 1: fetch assembly instruction from memory
  • Step 2: fetch into the CPU data in memory that the instruction requires (if applicable).
  • Step 3: execute arithmetic or binary operation (if applicable).
  • Step 4: evaluate conditions (if applicable)
  • Step 5: write results to memory (if applicable)

Now, if the CPU was waiting for all the steps to be over for the processing of an assembly opcode before starting processing of the next, that would be quite a waste since for most of the time the functionality in there would be available for use but not being used (in my example, the Arithmetic Processing Unit, which is what's used in step #3, would not be used during the time when the other steps were being done).

So what they did was get CPUs to process multiple opcodes in parallel, so in my example pipeline you would have on opcode on stage #1, another that already did stage #1 and is on stage #2 and so on, hence why I also called it an assembly line: at each step a "worker" is doing some work on the "product" and then passing it to the next "worker" which does something else on it and they're all working at the same time doing their thing, only each doing their bit for a different assembly instruction.

The problem with that technique is: what happens if you have an opcode which is a conditional jump (i.e. start processing from another point in memory if a condition is valid: which is necessary to have to implement things like a "for" or "while" loop or jumping over of a block of code in an "if" condition fails)?

Remember, in the my example pipeline the point at which the CPU finally figures out if it should jump or not is almost at the end of the pipeline (step #4), so everything before that in the pipeline might be wrong assembly instructions being processed because, say, the CPU assumed "no-jump" and kept picking up assembly instructions from the memory positions after that conditional-jump instruction but it turns out it does have to jump so it was supposed to be processing instructions from somewhere else in memory.

The original naive way to handle this problem was to not process any assembly instructions after a conditional jump opcode had been loaded in step #1 and take the processing of the conditional jump through each step of the pipeline until the CPU figured out if the jump should occur or not, by which point the CPU would then start loading opcodes from the correct memory position. This of course meant every time a conditional jump appeared the CPU would get a lot slower whilst processing it.

Later, the solution was to do speculative processing: the CPU tried to guess if it would the condition would be true (i.e. jump) or false (not jump) and load and start processing the instructions from the memory position matching that assumption. If it turned out the guess was wrong, all the contents of the pipeline behind that conditional jump instruction would be thrown out. This is part of the reason why the pipeline is organised in such a way that the result of the work only ever gets written to memory at the last step - if it turns out it was working in the wrong instructions, it just doesn't do the last step for those wrong instructions. This is in average twice as fast as the naive solution (and better guessing makes it faster still) but it still slowed down the CPU every time a conditional jump appeared.

Even later the solution was to do the processing of both branches (i.e. "jump" and "no-jump") in parallel and then once the condition had been evaluated throw out the processing for the wrong branch and keep doing the other one. This solved the speed problem but at the cost of having double of everything, plus had some other implications on things such as memory caching (which I'm not going to go into here as that's a whole other Rabbit Hole)

Whilst I believe modern CPUs of the kind used in PCs don't have this problem (and probably also at least ARM7 and above), I've actually been doing some Shader programming of late (both Computing and Graphics Shaders) and if I interpreted what I read correctly a version of this kind of problem still affected GPUs not that long ago (probably because GPUs work by having massive numbers of processing units which work in parallel, so by necessity they are simple) though I believe nowadays it's not as inadvisable to use "if" when programming shaders as it used to be a few years ago.

Anyways, from a programming point of view, this is the reason why C compilers have an optimization option of doing something called "loop unrolling" - if you have a "for" loop with a fixed number of iterations known at compile time - for example for(int i = 0; i < 5; i++){ /* do stuff */ } - the compiler instead of generating in assembly a single block of code with the contents of the "for" loop and a conditional jump at the end, will instead "unroll the loop" by generating the assembly for the body of the loop as many times as the loop would loop - so in my example the contents of that "for" loop would end up as 5 blocks in assembly each containing the assembly for the contents, one after the other, the first for i=0, the next for i=1 and so on.

As I said, it's been a long time since I've learned this and I believe nowadays general CPUs implement strategies to make this a non-problem, but if you're programming microcontrollers or doing stuff like Compute Shaders to run on GPUs, I believe it's actually the kind of thing you still have to take in account if you want max performance.

Edit: Just remembered that even the solution of doing the parallel execution of both branches doesn't solve everything. For example, what if you have TWO conditional jump instructions one after the other? Theoretically would need almost 4 or everything to handle parallel execution for it. How about 3 conditional jumps? "Is you nested for-loop screwing your performance? More news at 11!". As I said, this kind of stuff is a bit of a Rabbit Hole.

[-] Honytawk@lemmy.zip 30 points 1 month ago

Is his PhD in Electrical Engineering?

[-] MehBlah@lemmy.world 17 points 1 month ago

He is already standing too close and that stick would arc with that many volts flowing through it. The most likely outcome in reality if it had been energized. The arc would have jumped from the stick to him and no more New Zealand guy.

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[-] wowwoweowza@lemmy.world 13 points 1 month ago

Why people gotta hate on a movie three decades old that remains perfect?

[-] The_Picard_Maneuver@lemmy.world 12 points 1 month ago

Gotta meme to keep it alive

[-] billwashere@lemmy.world 12 points 1 month ago

Yep. Very domain specific knowledge but couldn’t pour piss outta a boot with the instructions on the heel.

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[-] Semi_Hemi_Demigod@lemmy.world 10 points 1 month ago

Even throwing a metal pipe against it won't do anything. Electric fences have one electrode in the ground, and that's how your body makes the circuit. If they had run and jumped onto the fence, then jumped off on the other side they would have been fine with the fences still active.

Source: I've set up an electric fence and been shocked multiple times, once through my head.

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this post was submitted on 26 Sep 2024
671 points (100.0% liked)

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