fivemack: (Default)
I recently bought some samples of rare-earth elements from elementsales.com - gadolinium, terbium and dysprosium - to play with their magnetic properties. They're supplied as coins inside plastic discs, since they're reasonably reactive.

The gadolinium behaves roughly as I was expecting it to; it's quite strongly attracted to a magnet when cold, and less so when hot. I thought the Curie point was a sharp phase transition and the material would be non-magnetic above 19C, but the material sticks to a magnet even if I've freshly taken it out of hot water. I've been a bit wary since the Curie point of NdFeB magnets is only about 80C; I should get hold of a more-robust magnet. eBay has a very limited range of SmCo2 magnets (most hits for samarium-cobalt are guitar pickups); possibly I just want a large iron bar magnet, but I'm not quite sure where to buy those in the real world.

The terbium and dysprosium, however, are also attracted to the magnet (the Dy less so than the Tb) at room temperature. It's a fairly fearsome magnet, so I suppose that the Tb and Dy have some traces of Gd left in them and that's what's being picked up; in which case I should try boiling them and seeing how the magnetism goes away. I need to think more about how to measure the forces here; I can't think of a setup with magnet, element, spring-balance and bits of string where I can just read off the force, and a model where I pull on a spring balance until the element comes free of the magnet seems impossible to get good readings from.

I imagine a note to the element supplier saying that they are supplying inferior gadolinium-laced terbium would not be useful; separating adjacent rare earth elements is proverbially hard.

Any advice on better magnets, better terbium, or better experimental setup?
fivemack: (Default)
Issue: What do I need to do to get a tape autoloader to work on an RHEL 3 machine

Answer: You need to install 'mtx' and 'sg3_utils' by doing 'up2date mtx; up2date sg3_utils', then reboot.

Issue: My computer running RHEL 3 (Red Hat Enterprise Linux 3) does not detect the media changer on my Quantum Superloader 3 tape library. Or it does not detect a WD MyBook USB hard drive, with /proc/scsi/scsi listing only the 'Enclosure' part.

Answer: http://spiralbound.net/2006/10/16/making-rhel-3-see-multiple-luns - you need to add a line to /etc/modules and rebuild your initrd to tell the kernel to look for multiple SCSI devices exposed by a single physical machine. Since USB, for added irritation, is part of the SCSI subsystem, this is also needed for USB peripherals that expose several USB devices.

By the way, the 'Enclosure' for a WD MyBook USB hard drive is the glowing blue button on the front.

Issue: Having done this, I get 'input/output error' messages from Amanda and 'st0: incorrect block size' messages appear in dmesg

Answer: You need to issue a 'mt -f /dev/nst0 setblk 0' command, possibly every time that you load a tape

Issue: mtx doesn't detect the mail-slot on my Quantum Superloader 3 tape library

Answer: No. It doesn't. Use the controls on the front to load and eject tapes from the library. Sorry.


It has taken two of us most of the day so far to answer these questions; Google gets inordinate numbers of references to the questions and very few to the answers. I *hope* that Google will now index this page and my successors will be able to get all of this at once.

BTW, do not mail john@globalphasing.net because we are using it as a spamtrap

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