fivemack: (Default)
I recently bought some samples of rare-earth elements from - 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)
We've just got a new machine at work on which I've been asked to install OpenSuSE 10.2 64-bit; this felt entirely straightforward.

Unfortunately, the default install of OpenSuSE doesn't include gcc. When I try installing gcc using YaST2, I get something which looks superficially like gcc, but which says 'gcc: error trying to exec 'cc1': execvp: No such file or directory' whenever I try to compile anything with it.

So, where's cc1 coming from? Deciding now would be a good time to use up some of the EU Assorted Symbol Mountain, I type

for i in /media/SU1020.001/suse/x86_64/*.rpm; do rpm -qpl $i | sed -e "s/^/${i//\//_}/g" | grep cc1; done

which tells me that /usr/lib64/gcc/x86_64-suse-linux/4.1.2/cc1 is provided by cpp41-4.1.2_20061115-5.x86_64.rpm

And indeed /usr/lib64/gcc/x86_64-suse-linux/4.1.2/cc1 exists on the machine. So, why isn't /usr/bin/gcc-4.1 finding it?

Normally strace comes to the rescue, but 'strace /usr/bin/gcc-4.1 -c foo.c' outputs many lines of the form

stat64(0x806b628, 0xff885abc) = -1 ENOENT (No such file or directory)

which are totally useless because strace is failing to dereference the pointer to the filename passed to stat64.

July 2017

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