OT: Saw a program on Leonard Lee last night

All i can say is wow. Was surfing the tube, and stopped on the discovery channel. They were talking about Leonard Lee developing a new scapel for plastic surgery, and a new method of holding wounds closed. The one that got me though was the mechanism for holding a hand open while it is operated on. My wife commented "Wow. I think those are the rare earth magnets your always playing with.
Was an excellent show, i missed the first part though. Just goes to show, a good idea is a good idea.
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Mo Sislac wrote:

It also shows that Leonard Lee is OBSESSED with rare earth magnets :-)
Hey, everyone neends a hobby :-)
BugBear
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I don't remember the circumstances but one day LOML saw me using a rare earth magnet from LV and was amazed. Fast forward a week or so - she comes home from shopping and couldn't wait to tell me that she saw a rare earth magnet used as the clasp mechanism on the front of a bra (brassiere, Jeff). I wonder if that was Leonard's idea.
Cheers, Mike

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On 5 Oct 2004 16:40:09 -0700, half snipped-for-privacy@hotmail.com (Mike) wrote:

Ouch !
I used to work at HP Labs, where every dilbertcage was issued with a handful of assorted magnets to stop us sticking pins in the walls. Naturally some people became collectors - they'd build cantilevered coathooks out of stacks of 3/4" magnets, all sorts of magnet-art.
Two hazards we discovered pretty soon were that a stack of big magnets flying together could blacken a fingernail, let alone raise pinch blisters. The second was that the magnets chipped easily, and peeling plating was razor sharp.
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Andy Dingley wrote:

Err. A stack of RE magnets could do awfully "interesting" and irreversible things to a colour CRT.
BugBear
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On Wed, 06 Oct 2004 14:16:57 +0100, bugbear

doesn't do a lot of good things for disks and other media storage, either..
Mac
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wrote:

It's much harder than you'd think. You can't kill magnetic media with externally applied magnetic fields, for most rational values of "field" and almost all possible fields from a permanent magnet. Distance is your enemy - even if you try to bulk demagnetise tape, you need to place tape _between_ pole pieces to achieve any reliable results.
One of the best sources for cheap rare earth magnets is scrap disk drives. Most contains two powerful ones, with large pole faces and normally mounted only a few mm from the disk itself.
CRTs are a _much_ easier target.
--
Smert' spamionam

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Andy Dingley wrote:

... and only used for the coil actutator. The disc surface is mag'd with a tiny coil that's *very* close to the disc.
BugBear
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mac davis wrote:

Years ago when floppies were actually floppy I was teaching an intro computer class, mostly college freshmen, some sophmores. One student came in complaining that something was wrong with her data on her disk. I inserted it in one of our Apple IIc's (yes, that long ago) and she was right, nothing could be read. I asked her how she stored the disk at home and she told me she kept it on the refrigerator with a magnet so she wouldn't lose it. Go figure.
Glen
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On Wed, 06 Oct 2004 14:16:57 +0100, bugbear

That's why we'd been issued with Test Managers. You could play "stick the magnet on the monitor" and see how many you could get there before PHB noticed.
--
Smert' spamionam

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The 14" woofer magnet did a pretty good job through the cube wall. The monitor was finally degaussed after a dozen or more on/off cycles.
Joel. phx

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On Wed, 06 Oct 2004 14:16:57 +0100, bugbear

An old girlfriend decided to clean my computer room one day and I came home to an unusable computer. The monitor was all screwy. I checked the cabling, R&Red the graphics card and cleaned the contacts, nothing helped. Then I noticed that she had put my electric clock directly over the screen, on a shelf 3 inches above the damned thing. Since _I_ hadn't moved the thing, and everything on my desk and shelves was all moved, I hadn't noticed it right away. Arrrrrrrrrrrrrgh!
Needless to say, she didn't clean my computer stuff again.
Say, do you think we could use the local hospital's $1.3Mil MRI to check for metal pieces in our boards? It should also remove the pieces of nail, etc., right?
--- - Friends don't let friends use FrontPage - http://diversify.com Dynamic Website Programming
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Nope. I worked at GE, on MRI scanners, for about 10 years. In that time there was, er, ample time for experimentation. It will not remove a metal sliver from a finger, although it does make it move around (to align with the flux lines) in a very uncomfortable way. It's disturbing to wear steel-toe shoes near an MRI magnet. You could scan the board to see the iron (it'd show up as a warpy-black-hole in the image). A pumpkin looks really cool on a 3D MRI scan, but if you scan it in "research mode" (no power limitation/monitoring) it turns soft by the next morning. Liquid helium is an interesting substance to work with, and superconductors can be very unforgiving.
So, yeah, you could _find_ the metal with the MRI scanner, and do a spectroscopic analysis of the lumber even, but it's not useful for removing anything. A hard drive rare earth permanent magnet has a strength of maybe 5 Tesla, where most MRI scanners are only at 1.5 Tesla (although with a _much_ larger field).
Dave "ask me what aluminum does in an MRI magnet...you'll be surpised" Hinz
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time

OK, what does aluminum do in an MRI magnet?
Dave Hall
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I was hoping someone would ask me that. It's non-magnetic, even at that field strength, but it's still electrically conductive. The flux lines in that magnet run lengthwise through the bore, and out and around the magnet in the shape you'd expect. But inside the bore, things get interesting. The field is _very_ even in there, or imaging wouldn't work. "even" down to "measured in parts per billion".
So anyway. Take an aluminum soda can. Not much weight, but a good diameter. Balance it on your fingertips and let it fall away from you. Tips over right away & falls down, as expected. Now do this in an MRI magnet, and it tips veerrrrrrrrrrryyyyyyy sllllllooooowwwwwlllllyyyyy until it's tipped enough to fall off your fingers, then falls at the expected speed. Tipping, you see, involves this conductive thing breaking flux lines. It sets up eddy currents inside the conductive item, and the electrons going around the soda can, while very low mass, are moving a lot of them at the same time. Keeps it from tipping, not sure if that's a gyroscopic effect or something else. Gravity, of course, works as expected.
A quarter takes maybe 1 second to tip over, a silver dollar about 3 seconds. But turn it 90 degrees (so the long part of the coin is in line with the flux lines / bore of the magnet) and it tips over as normal.
Fun stuff. Almost makes going back to GE sound attractive some days.
Dave "Almost..." Hinz
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On Thu, 07 Oct 2004 19:03:27 +0000, Dave Hinz wrote:

..snip..
Sounds like fun. The eddy currents induced in the Al come with their own magnetic fields, of course.
Are MRI machines' fields dipoles, quadrupoles, or something exotic? MRI is just NMR, right? (Organic chem was a looong time ago.)
Back on topic, had a thought while reading the Toolbox Book and the LV catalog in close succession: use the re magnets behind a felt layer for an invisible french fit. (not "fit" -- blanked on the correct term.)
--
"Keep your ass behind you"


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wrote:

Right, so I suppose it's those two opposing fields that slow down the tipping. On some of the test magnets, we had 2 foot square aluminum doors on the ends of them; opening them just involved hanging on, leaning, and waiting. It could _not_ be hurried. Good isometric exercise, though.

Dipole, north at one end of the bore, south at the other. It's the same as NMR but the "N" was dropped because the public gets scared by the "Nu-cyu-ler" word.

I kind of like the hidden latch/cow magnet idea myself. haven't used it yet though.
Dave
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Interesting. I really hope this idea catches on. And not just because I happen to have an industrial quality de-magnetizer.
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