Simon Bradshaw

Back in the day, I got first order predicate calculus, but skolemisation just make my brain hurt. (Combination of: hurried lecturer, lack of pure math background on my part, lack of time for me to read around the course.)

Gaah. I am now trying to convince myself that I do not need to go hunting for a refresher course.

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nmg.livejournal.com

The trick with skolemisation is understanding that the expressions before and after are only equivalent from the perspective of your theorem prover.

The corollary trick with skolem constants is understanding that, if you're told that a dog exists, it's okay to assume that it's your dog.

If you want a refresher, you're welcome to a copy of my teaching notes. Does this make me an enabler?

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gnommi.livejournal.com

did you tell them to use both sides of the paper
/1066andallthatquote

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surliminal.livejournal.com

My favourite exam question ever, back in the days when I taugt wills and succession, involved Prince Charles moving in with Camilla and trying to knock Di out his will while still providing for the children; it was a brilliant estate planning example! sadly the other people on the course insisted on me changing the names on the ground people might be offended!!!

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davidwake.livejournal.com

"The Man in the White Suit" - ahh, not seen that in ages, wonderful sound effects if I remember rightly. Patent would be tricky as he secretly made it using his employers time and resources.

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major-clanger.livejournal.com

Yes, the patent would almost certainly belong to Birnley Fabrics. In my problem I got around that by saying that Sidney was a self-employed inventor; my question was twofold:

- Did he disclose his invention before patenting it by wearing the white suit? (No, not if he doesn't actually disclose the process for making the fabric, and his patent application relates to that.)

- Is the following a suitable description of the process: “The fabric is made by reacting trinitrotoluene with dimethyl mercury, chlorine trifluoride and other ingredients in the presence of a catalyst at low temperatures and high pressures.” (No, it is woefully insufficient to teach another skilled practitioner how to work the invention.)

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Grat Cthulhu!

That mixture of ingredients would amount to the most serious industrial hazard known to man! No wonder this invention has never made it out of the lab (except as dangerously poisonous fragments after the explosion that killed the lead researcher and their entire team, as well as most of the company's headquarters staff).

Edited Date: 2010-02-19 01:01 pm (UTC)

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major-clanger.livejournal.com

Yes, I did come up with a carefully-selected list of ingredients. I took pleasure in explaining to my class of law undergrads just why TNT was by far and away the most benign of them...

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As a way of protecting your invention, it has this to recommend it: no competent chemist will attempt to reproduce the process.

Have you ever read an industrial chemist's blog on Things I won't work with? I am particularly impressed by Chlorine Tetrafluoride, which is described as 'Hypergolic with everything, including industrial chemists' and will ignite and burn quite cheerfully if spilt into a bucket of sand.

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major-clanger.livejournal.com

I will have to lend you John D Clark's Ignition! An Informal History of Liquid Rocket Propellants in which he describes CTF with the glee of someone who left most of the work with it to other people. He memorably sums it up thus:

"It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water — with which it reacts explosively. It can be kept in some of the ordinary structural metals-steel, copper, aluminium, etc.-because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminium keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes."

Clark goes on to describe an accident another research team had that involved spilling a ton of the stuff. It eat through a foot of solid concrete and three foot of gravel. One of its endearing qualities is that when it ignites on meeting your flesh, one of the combustion products is hydrofluoric acid, which dissolves bone and stimulates pain receptors. CTF, it's the gift that keeps on giving...

Edited Date: 2010-02-19 03:31 pm (UTC)

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Thank you for the correction: I should, indeed, have referred to the trifluoride.

That passage from Ignition! is widely quoted (and misquoted) but I have so far failed to obtain a copy of the book.

Obtaining it without ending up on anyone's database of potential terrorists would be a useful thing.

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It's available in reprographic form from the university -- costs about $50 in hardcover, printed to order, takes ten weeks to arrive. (I speak from experience.)

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coth.livejournal.com

There was an article about women working in munitions factories dying their hair blonde with the ingredients - TNT was mentioned, I think...

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Picric Acid, perhaps? IIRC it tends to dye things yellow (when it isn't going BOOM) ...

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Things I won't work with

Although I'm told that some of the items that feature in your own researches would constitute a serious Work Safety hazard, if they could be procured and examined in the laboratory. Feel free to write the COSHH assessment for a type IIa, or a Gamma-Ray Burster.

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I think they would also require an environmental impact statement (there would be no environment afterwards) before we got round to COSHH.

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CoSHH Leaflet for a visible sample of Neutronium?

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I'm not sure you can have a small lump of neutronium. A large gravitational mass may be necessary to prevent strong-force nuclear decay since it is, effectively, just a huge neutron rich nucleon.

It's something I'll have to think about sometime!

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Wouldn't a (hypothetical) small lump of neutronium rapidly undergo a phase change as some of the neutrons decayed into protons and electrons? And wouldn't the resulting degenerate matter tend to, um, undergo another phase change -- back into ordinary matter -- due to not having sufficient gravitational potential energy to overcome the electron degeneracy pressure?

I expect a lump of neutronium much less massive than a neutron star is indistinguishable from a very efficient fission bomb. The devil, of course, is in the detail: precisely how much less is the question!

(Things I would hate to see from inside the same solar system: a 100% efficient fission explosion involving, say, a lump of neutronium a metre or so in diameter. On the order of planetary mass, in other words.)

Edited Date: 2010-02-19 06:11 pm (UTC)

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Yes - I think you have it pretty much surrounded there. I'd have to do some calculations to work out the minimum stable mass, but suspect it might not be much off the Chandraseker limit.

Of course the same arguments apply to White Dwarf electron degeneracy supported matter, only without the radiological issues. I suspect this is the basis for the electron degeneracy bombs mentioned in some of Al Reynolds' work, but then he used to work on pulsars so would know.

This could all make an interesting exam question at some point in the future...

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Damn. I knew I'd left something out: the Lab Safety Sheet must list the risk of adding too much matter, leading to further collape and the formation of an event horizon.

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No, this would be a relatively inefficient fusion bomb: it falls well short of the theoretically-perfect bomb, which would convert all the available neutrons (and daughter protons) to iron then emit all the energy as electromagnetic radiation and kinetic energy.

The first inefficiency would be incomplete 'burnup' with very little of the fuel undergoing any fusion at all in a smaller bomb - and even in a larger one, an outer shell would simply be thrown off.

The second inefficiency would be nuclear synthesis, consuming energy in the formation of heavier elements at the core: I have no idea whether this is significant or not though. We'd need to ask a physicist, with some knowledge of supernovae, for estimates.

Overall, you'd get lots and lots of neutrons - like a 'Neutron Bomb', leaving buildings standing (actually, they don't), which is a very inefficient fusion bomb that discards half it's 'neutron budget' into the environment instead of fusing more nucleii or fast-fissioning the tamper.

Nevertheless, you're right in saying that a great deal of electromagnetic energy would be released if a small-ish neutronium body was 'de-confined'. But if you could build something to confine it in the first place, you might've built some *really* scary weapons.

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Fission bomb, not fusion. (Take one ginormous nucleus with atomic number equal to some large multiple of Avogadro's number; reduce to nucleons.)

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Oops. I should read comments more carefully before jumping in with a reply... And deconfined neutronium is, in a sense, the fission of a single giant nucleus - and, part-way through the process, you would observe lots of transuranic nucleii undergoing fission in a blizzard of neutrons.

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Also... Thinks of a scary weapon for alien space bats who can confine ten tons of Neutronium: put it in a chamber with reflective ends and make a laser... But the reflectors I'm thinking of are something like beryllium - which doesn't work here, as it cannot survive the forces involved, but there's a point I'm attempting to make about a neutron reflector.

The scary thing about David's electron-degenerate matter is that it's easier to manipulate and confine than neutron-degenerate matter. Admittedly, there are issues with generating magnetic fields that powerful - if they can impose electron-degeneracy, they can rip apart any conceivable conductor that generated them - But we are, at least, speculating about known physics rather than handwaving about materials or forces which remain outside all known theory.

A prediction: if ever we get up-close to a white dwarf and observe electron-degenerate matter, we'll observe weird, wacky, off-the-wall phenomena, every bit as unexpected as the discovery of superconductivity.

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Quite. I'm sure you have a number for the minmum stable mass of each form of degenerate matter scribbled down somewhere.

The Hazard sheet would need to list the risk of immediate implosion (of the laboratory and staff, and planet) into a thin layer of matter on the surface of the sample, followed by an intense burst of X-rays and the ejection of said laboratory, staff, etc into the surrounding space.

This raises interesting questions as to the most appropriate choice of protective gloves.

Specifying the container might be challenging: I'd just list a value for minimum tensile strength (for sub-stable samples requiring assisted confinement) and compression-resistance required to sustain the container against collapse onto the surface of the sample. This sidesteps impertinent questions about the laboratory, staff, and planet collapsing onto the container).

The best material would surely be neutronium but I suspect that this suggestion is unhelpful.

Radiological hazards... Your turn, I think.

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Here's one to think about, sometime: if you have a lump of neutronium that's just massive enough for gravity to maintain the collapsed state, how big a projectile would it take to spall off a fragment that would get far enough away to emerge from the degenerate state before it fell back?

Further, what if the impact split the neutron star up, hard enough that none of the fragments had the necessary gravity to exist as neutronium, and reverted to ordinary matter before the body could recombine?

Just one large fragment might dump enough energy into the remaining neutronium to destabilise it in a chain reaction that would liberate the entire mass in a very short time.

As weapons go, that's one for the BIG space opera.

Actually, unstable neutron stars are going to be rare: they form in an extremely energetic phase of stellar evolution, and I cannot see an unstable star surviving the process.

Edited Date: 2010-02-19 11:55 pm (UTC)

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Remind me to explain sometime how Larry Niven's known space universe gives us all the ingredients we need for supernova-pumped neutrino lasers ... (and yes, I mean taking the neutrino output of a supernova -- about an order of magnitude greater than its optical output -- and turning it into a directional beam).

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That'll be worth reading! Among other interesting technical questions: how will you get anyone to notice? It seems absurd to say that about a significant fraction of the output of a supernova, but that's the aloof neutrino for you. Reflecting the wimpish little sods would be a challenge to a laser cavity designer: my guess is that you've thought of something with a 'stepping disk' - or do stasis boxes reflect neutrinos?

Also from Known Space: interesting things you can do with scrith - a material with a tensile strength of the same order as the strong nuclear force. It might be just the thing for confining neutronium! It might even be neutronium, spread very thin; which raises the possibility that some arcane catalyst causes catastrophic disassembly.

The difficulty writing a coherent novel with this wonder stuff in it is not that it makes interesting things possible; it's that it makes everything possible and far too easy, wiping out the need for half the things you want your characters to do...

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Scrith is described as being opaque/reflective to 70% of neutrinos. QED.

Pick a massive star near the end of its life. Build a couple of scrith mirrors for the poles of the star, and a whole bunch of panels in eliptical orbits that will converge around the star, forming a very close ringworld around it. Use them to capture and pump a good chunk of the star's radiation back into the star. Wait for the supernova, then lase, baby, lase!

Note that at a distance of about 30 AU from a supernova, the neutrino flux is so intense that you could be hiding behind Jupiter and you'll still pick up a fatal radiation dose. And that's after doing the inverse square fandango over a spherical surface with radius measured in trillions of metres.

(The point about a neutrino laser is that nothing stops it. Except, ahem, scrith. What happens when a layer of scrith gets very hot, very fast? Paging Larry Niven ...)

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