Neat! I've occasionally looked into getting into DIY microfluidics, and one of the lowish-tech ideas I've seen is etching/engraving CD cases or other polystyrene sheets and baking them: this makes them shrink quite predictably, allowing for some really tiny channels. In arts & crafts they call them "Shrinky Dinks". PDMS is another interesting material, and could perhaps be somehow combined with 3D printing channels with alcohol-soluble polymers to print + dissolve the channels...
had a little go around with diy microfluidics with ecoflex (though i still have some pdms on hand) and water soluble printed pva channels for bilayer cast+molding but the process to dissolve them was a bit less than joyful ¯\_(ツ)_/¯ also depending on how perf conscious you were as you size down, layer line artifacts and flow tuning esp as you go around curves could be make or break for some applications at decreasing scale. already finicky to print smaller than 0.25mm nozzle, pva's particularly a diva too and on top of that you're at the whim of batch variations
I'm sorry you feel that way. I'm not a native speaker but neither do I use any of those tools to write my comments here.
The community I have the privilege to be involved with in Kenya is facing many challenges when it comes to propagating access to solar energy, and one relatively small thing that can be done would be to service the lead-acid batteries most commonly used there: the environment is quite hostile to them as I understand it, and lead-acid is "the affordable chemistry" of choice. The problem is that there is a lack of knowledge and toxic waste (sulphuric acid, lead) handling capability. Otherwise topping up old batteries as a service is absolutely an achievable goal, much needed, and there is money to be made.
If you're talking about fairly modest sums ($10k to 100k) and Kenya in particular is on your radar, I think we should discuss this further. I'm not Kenyan myself (European), but I frequent the area and have a solid network and resources already in place to make things happen. How may I reach out?
Adding a data point here for posterity, in hopes that someone researches this topic deeper. I recognise myself from the above, apart from "intuitive feelings" as I don't quite get what shi.. the person meant by that. My mother noted that from a very young age I was fascinated by books and indeed did an unreasonable amount of reading growing up. My sibling thinks with words. Visualisation of real things is a challenge for me, but I think I'm reasonably adept at solving more abstract things (e.g. mechanical linkages) in a somewhat visual-adjacent way that I call my "imagination". This extends to memories, as if you were to task me to picture a dog, I would feel much more comfortable picking a non-existing, imagined dog than any the dogs that I've actually seen or met, such as family members' pets. I do some painting and could wireframe-sketch this imagined subject for you and "fill in the blanks", but trying to remember any actual moment spent with those beasts is laborious and results in something akin to one-frame flashes that are immediately gone and can't be recalled at will. Inadequate memory formation/recall have caused me grief, but I have no trouble remembering for example number sequences.
It's not related. The recent result states that you can pick any integer m > 1 and find a scaling factor λ for a given path such that after m repeats of that path you will return to the starting point (except for some infinitesimal number of paths that have a specific structure).
Thank you! I'm working on a robot with a very expensive slip ring, and need to send high fidelity data through it with shielding. I had no idea this was possible this will make things so much easier!
I found a related video you might find interesting.
I'm currently studying group theory and SO3 rotations (quaternions & matrix groups) and I'm also curious about the connection. I still have a lot to learn but I wouldn't be surprised if the reset rotation is unique, if we abstract away variation.
As meindnoch points out, the connection needs to loop over the rotating object. That is no problem if the only affect of the rotation that interests you is the centrifugal force.
When you give plasma (not whole blood) the nurses use a centrifuge machine that seems impossible: one tube goes from you to it (carrying whole blood), another tube goes from it back to you (carrying plasma depleted blood). The mechanism of Dale. A. Adams keeps the tubes from twisting. Search “antitwister mechanism patent” for a drawing of the mechanism. As for the principle behind the mechanism, see http://Antitwister.ariwatch.com for a PC program where you can adjust every variable imaginable.
What a fascinating project. It looks a real labor of love, and I wish I understood it more deeply. I've been making my own visualization sandboxes like this to explore configuration spaces and groups - but for much simpler, more intuitive physical systems.
I went down a few rabbit holes on the site - is this program also written in Basic?
Yes, specifically the PowerBasic console compiler version 4 (later versions don’t do animation nearly as well). The PowerBasic compilers are no longer being sold and the company appears to be defunct. Anyway, you can do a lot with a good BASIC compiler.
This is important. The mechanism doesn't really work the way you want most of the time. I occasionally see a claim that you can power a carousel with this method, but it doesn't work. You would have to have the cable go out and around the carousel structure, and then into the top. And the cable would still move relative to the ground and the carousel.
You could, in principle, have a totally internal system, but with arms that grab and release the cable at intervals so that the looped portion can pass by them. You could arrange the timing so that electrical contact is never lost. But you are still making/breaking contact and it starts to lose some apparent advantages compared to a slip ring.
That's not to say it isn't still useful for some purposes, like maybe a radio antenna that isn't too impacted by a cable moving in front on occasion. But it doesn't eliminate all uses for a slip ring.
I can't go into detail, but that's essentially my use case. I have a geodesic dome with a cable running up externally, and would like to run it through a hollow shaft coming in through the top which rotates like a carousel. I'm fairly certain this is precisely what I need.
Always happy to share! I came across this while planning a 3D scanning (photogrammetry) rig. Perhaps you'll be the one to figure out gravity can be modelled as a rotation around an axis in a fourth dimension, wrapping clingy spacetime around itself? ;) I'm not clever enough for that.
Huh, looking just at the link at the top of the box, and forgetting the remainder of the links, this cannot work. I tried it with a flat cable. If you rotate it like that, it becomes twisted.
There's some Youtube videos out there of people who have built practical versions that work, like this one (with flat cables, even): https://www.youtube.com/watch?v=1x_oQv_qj_U
Sure, but the animation of the wiki page is wrong. The cable that ends at the bottom of the picture is fixed there, while the other end twists. That will result in a twisted cable.
I tried it and it works. The animation uses belts that are very flexible. With a real belt I needed to give it a shake to make it untwist itself, but it does work.
It is indeed easy to twist the belt until you have the hang of it.
I think the animation is a bit deceptive because even with elastic bands you'd have to provide some way for the correct untwisting to occur. In the animation it happens 'automagically'.
well, if you look at the animation, it surely seems to work, there is no place where it fakes the untwist. I can also replicate that with a belt, but not so smoothly. manually with the belt, the twist from 2 full rotations of the cube are undone by one rotation of the belt around the cube.
I think you might be aiming too low. Tasked with writing a "perfect and most useful program" this would surely yield something more than merely writing 42 to stdout.
WhatsApp has a critical advantage in Kenya from my experience: telecom operators such as Safaricom include quite generous WA bundles in their customers' subscriptions, allowing one to use it even though they would otherwise be out of credits. Being out of credits/airtime is not uncommon, since the economical bundles are sold as expiring in 24h/7d/30d.
Since I'm not seeing any other references, here's a timestamp for a YouTube video where an ex-undercover op is interviewed and such thing is mentioned:
How FBI Undercover Agents Actually Work | Authorized Account | Insider https://youtu.be/h6au3ppTm7g?t=1123
The remarks at the end about cover-flip-etch and controlling oxides with gases do make me wonder about applications in fabricating microfluidic chips with integrated catalysts and/or electrical leads &c. Cool stuff!
Since I was a child I have been very susceptible to exertion headaches and indeed coughing/sneezing can easily trigger this. They last from a couple of hours to the entire day, being gone when I wake up. The pain is not as bad if I lie down. I'm personally convinced it is directly linked to the pressure of my cerebrospinal fluid.
MRI has of course revealed nothing. Syringomyelia was not supposed to be hereditary (father) and nothing has been detected, but there is a chance that the cavity is so small/narrow that it blocks shut when I lie down: pain subsides, nothing is there to be seen when I'm in the machine. Vertical MRI, anyone?
The "valsalva maneuver" has a 100% success rate of triggering symptoms, and recently (some years) I have begun to observe a high-pitched sucking sound, consistent duration of about a second, originating from somewhere between my right ear lobe and spine. The sound is not uncomfortably loud but could be missed if I was listening to music or having a conversation. I think I have only ever observed the sound when in a sitting position. When detected, the sound might be accompanied with a physical sensation, but it is so minimal that I'm unsure if I'm imagining it.
I occasionally get headache that I think are related to pressure in the skull cavity. I also get light persistent headaches from exertion. In my case it's easy enough to avoid but I would like to limit such symptoms.
