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Paper Centrifuge

gizmodo.com

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Re: Paper Centrifuge

#71

Post by calvinlh »

readhn wrote: post #25

its a nice toy, for kids to learn science. but really, what are we - stuck in the stone age? Its year 2017, there is no reason why those people should not have access to the advanced technology we enjoy today in the west. make a pathetic paper centrifuge and give ourselves a pat on the back, really? What have we become?

Currently, there is absolutely no realistic way to set up the infrastructure required to operate such labs in third world countries. The costs would be astronomical.

While, yes, ideally all humans would receive the same high standard of healthcare, pragmatically it's just not going to happen anytime soon. Before that happens, this is a very useful (and clever) tool.

Re: Paper Centrifuge

#72

Post by burntwater »

readhn wrote: post #40
hx87 wrote: post #39

Earlier quoted context omitted.

> kill one of those multibillion military projects and redirect the money And how are the inventors supposed to do that?

we, the citizens who vote are supposed to do that.

And what happens if the people I vote for, who are supposed to fix this situation, don't win the election? Should I just sit around for a couple more election cycles and do nothing?

Re: Paper Centrifuge

#73

Post by Florin_Andrei »

JohnJamesRambo wrote: post #65
tejtm wrote: post #61

Earlier quoted context omitted.

Wouldn't the g-force direction always be the same (away from the center) regardless of direction of spin and zero at the inflection between spin directions (normal gravity excepted)?

If you have something slung on one side of the tube, it will rapidly want to go to the other side of the tube as the centrifuge switches direction on the reverse spin.

1. The g-force always acts in one direction: towards the outside of the disc.

2. The diameter of the tube is small. It's nearly 1-D dynamics in there.

3. Very large g-forces only happen at top rotational speeds. When not rotating, the material gets slowly mixed back up, but at the regular (i.e. very slow) diffusion speed.

So: separation works always towards the outside + re-mixing is a much slower process = it works as expected.

Re: Paper Centrifuge

#74

Post by Florin_Andrei »

Declanomous wrote: post #13
bluetwo wrote: post #11

Cool idea but it can't possibly be safe to spin infected blood on a device such as this.

I don't know why it would be any more dangerous than a typical centrifuge. Samples are in a vial, and that vial is what is responsible for containing the sample while you spin the samples. Having been around conventional centrifuges that have been destroyed due to improper balance, I assure you that any way you can imagine infected blood being distributed by the paper model would be 10x worse with a normal centrifuge…

Eh, both of you are right.

Yes, a full-blown centrifuge could be made safer (put a shield around it, yadda-yadda). But if the paper device is made safe enough, I don't see why it should not be used when there are no better options. And it appears that it could be made safe enough.

Re: Paper Centrifuge

#75

Post by khedoros1 »

readhn wrote: post #27

whats next? a fake life size cut out image of a doctor with a smartphone attached to it for a speaker? its sad that people have to die because they don't have access to the technology that's not that expensive and readily available in the "developed countries". And now we have to come up with some pathetic paper gizmos to justify our actions? Are we really that developed? Seems to me that we are going backwards...

> technology that's not that expensive

"Expensive" is relative, and the technology has extra costs outside of itself that have been paid in some parts of the world, but not in others. In a part of the world where electricity may as well be unobtainium, that heavy, carefully-calibrated, $1000 centrifuge isn't much better than the scrap value of the metal it's made from (while still being obscenely, prohibitively expensive for the people it would help).

> justify our actions

Who's talking about justification, besides you? There isn't anything to justify.

> Are we really that developed?

We've got shinier toys, if you want to call that "developed". We haven't improved upon the human race itself, if that's what you mean. Humans are naturally selfish and tribal. Society shifts tribal boundaries, and social structures like government can force selfishness into a longer-term view, but that's about all.

Re: Paper Centrifuge

#76

Post by JohnJamesRambo »

Florin_Andrei wrote: post #73
JohnJamesRambo wrote: post #65

Earlier quoted context omitted.

If you have something slung on one side of the tube, it will rapidly want to go to the other side of the tube as the centrifuge switches direction on the reverse spin.

1. The g-force always acts in one direction: towards the outside of the disc. 2. The diameter of the tube is small. It's nearly 1-D dynamics in there. 3. Very large g-forces only happen at top rotational speeds. When not rotating, the material gets slowly mixed back up, but at the regular (i.e. very slow) diffusion speed. So: separation works always towards the outside + re-mixing is a much slower process = it works…

Yes I understand what you are saying, that the force is going to the outside of the disc, but using even light braking (over minutes or even hours for ultracentrifuging) can disturb a pellet or separation. This is rapidly coming to a complete stop and reversing direction over and over.

Re: Paper Centrifuge

#77

Post by tbabb »

nneonneo wrote: post #41

As usual, what you really want to do is read the paper: http://www.nature.com/articles/s41551-016-0009 This is a well-written and very clear paper. It covers several aspects that went unmentioned in the Gizmodo article, and highlights that although building such a device may be trivial, evaluating and studying it is not. Some highlights: the paper covers how the device was built in detail, including information on th…

Holy crap. 125,000RPM for a 5mm disc means the edge is spinning at nearly 9,000mph.

On top of that, the g-force would be

    a = v^2 / r 
    v = 2 * pi * 5mm * 125000/60 s^-1`
    r = 5mm
...giving 87,000 gees?!

I start to wonder if general relativity effects (frame-dragging?) start to become noticeable at that acceleration.

Re: Paper Centrifuge

#78

Post by lb1lf »

Declanomous wrote: post #13
bluetwo wrote: post #11

Cool idea but it can't possibly be safe to spin infected blood on a device such as this.

I don't know why it would be any more dangerous than a typical centrifuge. Samples are in a vial, and that vial is what is responsible for containing the sample while you spin the samples. Having been around conventional centrifuges that have been destroyed due to improper balance, I assure you that any way you can imagine infected blood being distributed by the paper model would be 10x worse with a normal centrifuge…

True story: The company I work for make some pretty hefty winches for offshore use. Think ROVs, subsea oil installation, salvage &c.

Years ago, one of our customers had ignored a number of increasingly strongly worded safety bulletins, the end result being that just as they were going to hoist their megabuck ROV back aboard, the winch motors stopped and - for an encore - it turned out they hadn't tested the brake in ages, either - so it was incapable of halting the winch.

Now, the ROV itself would very gently drift towards the bottom. Too bad the umbilical cord between it and the winch weighs several kilos per meter.

The initial yank as the ROV freefell to the sea surface and the inertia of the drum ensured enough cable was paid out for the weight of it to keep the winch going faster and faster. Basically you had a very large loop with the ROV at one end, the winch at another.

This drum was designed for some 30rpm or so at the maximum design speed. Based on a video from a surveillance camera, we found the drum did close to 200 rpm as a few tons of cable pulled at it.

At this point, thinking the brakes must have been stuck disengaged, some brave soul with poor judgment and an axe appears, chopping off the hydraulic hoses to the brake. Lucky for him, the brakes weren't able to stop the thing anyway - otherwise, he would have found out if the designers had made the frame sturdy enough to remain intact during the retardation which would have followed.

This brave soul then realises that the game will be up in a few moments' time anyway - when the drum runs out of cable, at which point being anywhere near the winch will be very bad for you.

He runs like mad, disappear from the frame and then, seconds later - kerrrr-whaaang as the umbilical is ripped from the drum, the drum is torn from the frame and it all disappears into the large, blue waste disposal.

That led to a quite interesting post mortem. They found assorted bits and pieces of the winch all over the deck.

Somewhat off topic, but disintegrating centrifuges got me started...

Re: Paper Centrifuge

#80

Post by DanBC »

lb1lf wrote: post #78
Declanomous wrote: post #13

Earlier quoted context omitted.

I don't know why it would be any more dangerous than a typical centrifuge. Samples are in a vial, and that vial is what is responsible for containing the sample while you spin the samples. Having been around conventional centrifuges that have been destroyed due to improper balance, I assure you that any way you can imagine infected blood being distributed by the paper model would be 10x worse with a normal centrifuge…

True story: The company I work for make some pretty hefty winches for offshore use. Think ROVs, subsea oil installation, salvage &c. Years ago, one of our customers had ignored a number of increasingly strongly worded safety bulletins, the end result being that just as they were going to hoist their megabuck ROV back aboard, the winch motors stopped and - for an encore - it turned out they hadn't tested the brake in…

There are some videos on youtube of anchors dropping too fast:

https://www.youtube.com/watch?v=hvrgFPcPXfo

https://www.youtube.com/watch?v=RAcfaMDcY68

https://www.youtube.com/watch?v=b7pRfix_sNg

It's pretty scary.

(Someone else posted one of these links originally, I'll try to find it)

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